MHB Solve Segmentation Fault: Destroy Planetary System "Solid

Nono713 · Dec 2, 2014

GCC 3.4.4 was released in mid 2005, almost a decade ago. GDB 6.8 is from early 2008, and you have the cvs (snapshot?) version. They were most definitely not meant for each other. Please, mathmari, do yourself a favour and upgrade your toolchain. Trying to use broken tools is just not worth it.

mathmari · Dec 5, 2014

I downloaded Cygwin again I chose the following packages that should be satisfied:

[m]ca-certificates (2.1-1)
CA root certificates
Required by: libopenssl100

cygwin-debuginfo (1.7.33-1)
Debug info for cygwin
Required by: cygwin64-gcc-debuginfo, gcc-debuginfo, gdb-debuginfo, cygwin-debuginfo

cygwin-devel (1.7.33-1)
Core development files
Required by: gcc-core

libargp (20110921-2)
Interface for parsing command line arguments
Required by: getent

libatomic1 (4.8.3-4)
GCC C11/C++11 locked atomics runtime library
Required by: gcc-core

libcharset1 (1.14-2)
GNU character set conversion library and utilities - runtime (2)
Required by: libiconv

libcloog-isl4 (0.18.0-2)
CLooG Chunky Loop Generator (runtime)
Required by: gcc-core, gcc-g++

libdb4.8 (4.8.30-1)
Oracle Berkeley DB (db4.8 - C and C++ libs)
Required by: perl, python

libffi6 (3.0.13-1)
Portable foreign function interface library
Required by: python, libp11-kit0

libgmp10 (6.0.0a-1)
Library for arbitrary precision arithmetic (C runtime)
Required by: coreutils, gawk, gcc-core, gcc-g++, libmpfr4, libcloog-isl4, libisl10, libmpc3, mingw-gcc-g++, mingw-gcc-core

libgomp1 (4.8.3-4)
GCC OpenMP runtime library
Required by: gcc-core

libiconv (1.14-2)
GNU character set conversion library and utilities
Required by: man-db, libintl-devel

libintl-devel (0.18.3.2-2)
GNU Internationalization runtime library
Required by: libuuid-devel

libisl10 (0.11.1-2)
Integer Set Library (runtime)
Required by: gcc-core, gcc-g++

libmpc3 (1.0.2-1)
C library for multiple-precision floating-point computations with exact rounding (runtime)
Required by: gcc-core, gcc-g++, mingw-gcc-g++, mingw-gcc-core

libmpfr4 (3.1.2-1)
A library for multiple-precision floating-point arithmetic with exact rounding (runtime)
Required by: gawk, gcc-core, gcc-g++, libmpc3, mingw-gcc-g++, mingw-gcc-core

libopenssl100 (1.0.1j-1)
A general purpose cryptography toolkit with TLS implementation (runtime)
Required by: python, lynx, perl_vendor

libp11-kit0 (0.20.7-1)
PKCS#11 module library
Required by: p11-kit

libpcre1 (8.35-1)
Perl Compatible Regular Expressions UTF-8 runtime
Required by: grep

libpipeline1 (1.3.0-3)
C library for manipulating pipelines of subprocesses - runtime.
Required by: man-db

libquadmath0 (4.8.3-4)
GCC Quad-Precision Math runtime library
Required by: gcc-core

libsmartcols1 (2.25.2-1)
Tabular data formatting library (runtime)
Required by: util-linux

libsqlite3_0 (3.8.7.2-1)
An embeddable SQL database engine (library)
Required by: python

libtasn1_6 (4.2-1)
Tiny ASN.1 library (runtime)
Required by: p11-kit, p11-kit-trust

libuuid-devel (2.25.2-1)
Universally Unique ID library (development)
Required by: python

libxml2 (2.9.2-1)
GNOME XML library (runtime)
Required by: perl_vendor

lynx (2.8.7-1)
Text-based Web browser
Required by: man-db

mingw-binutils (2.23.1-1)
Binutils for MinGW.org Win32 toolchain
Required by: mingw-gcc-core

mingw-gcc-core (4.7.3-1)
GNU Compiler Collection (C, OpenMP)
Required by: mingw-gcc-g++, mingw-gcc-g++

mingw-gcc-g++ (4.7.3-1)
GNU Compiler Collection (C++)
Required by: gcc-mingw-g++

mingw-pthreads (20110507-2)
Libpthread for MinGW.org Win32 toolchain
Required by: mingw-gcc-core

p11-kit (0.20.7-1)
PKCS#11 module tool
Required by: ca-certificates

p11-kit-trust (0.20.7-1)
PKCS#11 module library
Required by: ca-certificates

perl_vendor (5.14.2-3)
Additional vendor modules previously packaged in perl-5.10
Required by: texinfo

popt (1.16-1)
Library for parsing cmdline parameters
Required by: libpopt0

python (2.7.8-1)
Python language interpreter
Required by: gdb

tcl (8.5.11-1)
Tool Command Language
Required by: tcltk

vim-common (7.4.527-1)
Vi IMproved - enhanced vi editor (common runtime)
Required by: vim

w32api-headers (3.3.0-2)
MinGW-w64 Windows API headers for Cygwin
Required by: gcc-core, w32api

w32api-runtime (3.3.0-1)
MinGW-w64 Windows API import libraries for Cygwin
Required by: gcc-core, w32api

windows-default-manifest (6.4-1)
Default Windows application manifest
Required by: gcc-core

xxd (7.4.527-1)
Hexdump utility
Required by: vim-common

zlib-devel (1.2.8-3)
Gzip de/compression library (development)
Required by: binutils

_autorebase (000713-1)
Run rebaseall automatically
Required by: cygwin, file, gawk, gcc-core, libblkid1, libgcc1, libssp0, libstdc++6, libuuid1, man-db, mingw-runtime, perl, zlib0, libgmp10, libatomic1, libgomp1, libmpc3, libquadmath0, python, libpcre1, libpipeline1, perl_vendor, libsmartcols1, libopenssl100, libsqlite3_0, libxml2, p11-kit-trust, libp11-kit0, libtasn1_6
[/m]

Are these the correct one?? (Wondering)

I like Serena · Dec 5, 2014

mathmari said:

Are these the correct one?? (Wondering)

I hope so! (Doh)

Does it work now? (Wondering)

mathmari · Dec 5, 2014

Yes, it works now! (Smile)

For [m]gcc -v[/m] I get:

[m]Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/i686-pc-cygwin/4.8.3/lto-wrapper.exe
Target: i686-pc-cygwin
...
gcc version 4.8.3 (GCC)[/m]

and for [m]gdb -v[/m] I get:

[m]GNU gdb (GDB) 7.8
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-pc-cygwin".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".[/m]

mathmari · Dec 6, 2014

When I write now [m]gcc -g main.c stars.c[/m] and then [m]gdb a.exe[/m] and [m](gdb) r[/m] I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe
[New Thread 2460.0xa08]
[New Thread 2460.0x1098]
Usage: /a <input_file>
[Thread 2460.0x1098 exited with code 1]
[Inferior 1 (process 2460) exited with code 01][/m]

What does this mean?? (Wondering)

Nono713 · Dec 6, 2014

Seems like your program a.exe wants an input file, and is printing out its usage information... what does your main function look like, and have you tried following the instructions it's giving you and trying:

Code:

gdb a.exe <input_file>

where <input_file> is to be replaced with a suitable input file, I have no idea what that would be, I haven't followed the thread which is a bit of a mess anyway, it would help a lot if you posted your entire program.

I like Serena · Dec 6, 2014

Bacterius said:
Seems like your program a.exe wants an input file, and is printing out its usage information... what does your main function look like, and have you tried following the instructions it's giving you and trying:
Code:
gdb a.exe <input_file>
where <input_file> is to be replaced with a suitable input file

Indeed!

However, the command should be:

Code:

gdb --args a.exe input.txt

Otherwise the input file is interpreted as a core dump. (Wasntme)

mathmari · Dec 6, 2014

Ok! Now I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 2072.0x1674]
[New Thread 2072.0x93c]

...

Program received signal SIGSEGV, Segmentation fault.
0x004024e6 in destruction (solid=7620203, gap=5000) at stars.c:309
309 sum=sum+f->gap;
[/m]

Why do I get a segmentation fault at this point?? (Wondering) The function destruction() is the following:

Code:

int destruction(int solid, int gap){
	int ffplanpos=-1;
	int i, j;
	int sum=0;
	asteroid_t *planf = calloc(1, sizeof(asteroid_t));
	asteroid_t *K=NULL;
	asteroid_t *f=NULL;
	plansys_t *p=NULL;
	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->solid != solid){
			p=p->next;
			j=i;
		}
	}
	if(p == NULL){
		printf("The planetary system with identifier %d couldn't be found\n", solid);
		return -1;
	}
	f=p->asteroids;
	while(sum<gap){
		sum=sum+f->gap;
		f=f->next;
		DELETE(f->prev, f->prev->as);
	}
	

	for(i=0; i<max; i++){
		if(StarS[j].ffplan[i].fp == INT_MAX){
			ffplanpos=i;
		}
	}
	
	if(ffplanpos == -1){
		return -1;
	}
	
	StarS[j].ffplan[ffplanpos].fp=solid;
	
	
	planf->as=f->as;
	planf->gap=0;
	planf->next=NULL;
	planf->prev=NULL;	f=f->next;
	while(f != NULL){
		if (StarS[j].ffplan[ffplanpos].ff == NULL) {
        	StarS[j].ffplan[ffplanpos].ff = planf;
        } else {
        	asteroid_t *last = StarS[j].ffplan[ffplanpos].ff;
        	while (last->next != NULL) {
        		last = last->next;
        	}
        	last->next = planf;
       	}     
	f=f->next;
	}     
	
	
	printf("\n\nPlanet Systems = ");
	
	while(StarS[j].plasy != NULL){
		printf(" %d ", StarS[j].plasy->solid);
		StarS[j].plasy=StarS[j].plasy->next;
	}
	
	printf("\n\nFree-floatingM = ");
	
	for(i=0; i<ffplanpos; i++){
		printf(" %d ", StarS[j].ffplan[i].fp);
	}
	
	printf("\n\nFree-floating planets = ");

	
	for(i=0; i<=ffplanpos; i++){
		while(StarS[j].ffplan[i].ff != NULL){
			printf(" %d ", StarS[j].ffplan[i].ff->as);
			StarS[j].ffplan[i].ff=StarS[j].ffplan[i].ff->next;
		}
	}

	return 0;
	
}

I like Serena · Dec 6, 2014

mathmari said:

[m]Program received signal SIGSEGV, Segmentation fault.
0x004024e6 in destruction (solid=7620203, gap=5000) at stars.c:309
309 sum=sum+f->gap;
[/m]

Why do I get a segmentation fault at this point?? (Wondering)

Because you are trying to dereference [m]f[/m] when it is not a valid pointer. (Doh)

Shouldn't there be a check whether [m]f[/m] is NULL or not? (Wondering)

mathmari · Dec 6, 2014

I like Serena said:

Because you are trying to dereference [m]f[/m] when it is not a valid pointer. (Doh)

Shouldn't there be a check whether [m]f[/m] is NULL or not? (Wondering)

I added the check

Code:

if(p->asteroids == NULL){
		printf("The planetary system doesn't contain any asteroids\n");
		return 0;
	}

Now I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 5184.0x13f4]
[New Thread 5184.0x798]

...

The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 5184.0x798 exited with code 0]
[Inferior 1 (process 5184) exited normally][/m]

But why doesn't it contain any asteroids?? (Wondering)

Didn't we add the asteroids with the following function??

Code:

asteroid_t *asteroid_constitution(int as, int gap, int solid){
	int i, g=0;
	asteroid_t *ast = calloc(1, sizeof(asteroid_t));
	ast->as=as;
	ast->gap=gap;
	ast->prev=NULL;
	ast->next=NULL;
	plansys_t *p=NULL;
	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->solid != solid){
			p=p->next;
		}
	}
	if (p->asteroids==NULL){
		p->asteroids=ast;
	}
	else{
                asteroid_t *last=p->asteroids;
                asteroid_t *q=NULL;
                asteroid_t *previous=NULL;
                if(ast->gap < last->gap){
                        ast->prev=NULL;
                        ast->next=last;
                        last->prev=ast;
                        last->gap=last->gap-ast->gap;
                        p->asteroids=ast;
                }
                else{
	                while(g < ast->gap && last->next != NULL){
	                	g=g+last->gap;
                                previous=last;
                                last=last->next;
                }
                if(last != NULL && last->next==NULL){
                        ast->prev=last;
                        ast->next=NULL;
                        last->next=ast;
                        ast->gap=ast->gap-g;
                }
                else{
                        ast->next=last->next;
                        last->next->prev=ast;
                        ast->prev=last;
                        last->next=ast;
                        ast->gap=ast->gap-g;
                        q=ast->next;
                        q->gap=q->gap-ast->gap;
            }
        }
    } 
    return 1;
}

(Wondering)

I like Serena · Dec 6, 2014

mathmari said:

[m]The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 5184.0x798 exited with code 0]
[Inferior 1 (process 5184) exited normally][/m]

But why doesn't it contain any asteroids?? (Wondering)

Didn't we add the asteroids with the following function??

Which information do you have in your [m]file.txt[/m] regarding solid=7620203 and gap=5000? (Wondering)

Suppose you add:

Code:

	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->solid != solid){
			p=p->next;
		}
	}
        printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
                as, gap, solid, p);[/color]
	if (p->asteroids==NULL){

What is the output that you get regarding solid=7620203? (Wondering)

mathmari · Dec 6, 2014

I like Serena said:

Which information do you have in your [m]file.txt[/m] regarding solid=7620203 and gap=5000? (Wondering)

The file.txt is the following:

[m]I
C 762
B 7620213 762
B 7620203 762
A 987 4232 7620203
A 985 1232 7620203
A 986 6344 7620203
D 7620203 5000
[/m]

When I write [m](gdb) r[/m] I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 6136.0xcc0]
[New Thread 6136.0x1408]

I OK
C 762
StarSystems = 762
OK
B 7620213 762
PlanetarySystems = 7620213
OK
B 7620203 762
PlanetarySystems = 7620213 7620203
OK
A 987 4232 7620203
987 : 4232 : 0 : 0

OK
A 985 1232 7620203
985 : 1232 : 0 : 0

OK
A 986 6344 7620203
986 : 6344 : 0 : 0

OK
The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 6136.0x1408 exited with code 0]
[Inferior 1 (process 6136) exited normally][/m]

I like Serena said:

Suppose you add:

Code:

	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->solid != solid){
			p=p->next;
		}
	}
        printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
                as, gap, solid, p);[/color]
	if (p->asteroids==NULL){

What is the output that you get regarding solid=7620203? (Wondering)

When I add the command [m]printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
as, gap, solid, p);[/m]
I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 6052.0x14f4]
[New Thread 6052.0xe80]

I OK
C 762
StarSystems = 762
OK
B 7620213 762
PlanetarySystems = 7620213
OK
B 7620203 762
PlanetarySystems = 7620213 7620203
OK
asteroid_constitution(as=987, gap=4232, solid=7620203) p=0x80059918
A 987 4232 7620203
987 : 4232 : 0 : 0

OK
asteroid_constitution(as=985, gap=1232, solid=7620203) p=0x80059918
A 985 1232 7620203
985 : 1232 : 0 : 0

OK
asteroid_constitution(as=986, gap=6344, solid=7620203) p=0x80059918
A 986 6344 7620203
986 : 6344 : 0 : 0

OK
The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 6052.0xe80 exited with code 0]
[Inferior 1 (process 6052) exited normally][/m]

(Wondering)

I like Serena · Dec 6, 2014

mathmari said:

When I add the command [m]printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
as, gap, solid, p);[/m]
I get the following:
(Wondering)

I believe this is the location where your problem is.
The code to find the right [m]p[/m] is wrong.
It will always choose the last star system, instead of the one with the matching [m]as[/m]. (Worried)

mathmari · Dec 6, 2014

I like Serena said:

I believe this is the location where your problem is.
The code to find the right [m]p[/m] is wrong.
It will always choose the last star system, instead of the one with the matching [m]as[/m]. (Worried)

I changed something...

Code:

for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p->next != NULL && p->solid != solid){
			p=p->next;
			k=i;
		}
	}
	
p=StarS[k].plasy;
	
printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
                as, gap, solid, p);

Now I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 4860.0x1668]
[New Thread 4860.0x13d0]

I OK
C 762
StarSystems = 762
OK
B 7620213 762
PlanetarySystems = 7620213
OK
B 7620203 762
PlanetarySystems = 7620213 7620203
OK
asteroid_constitution(as=987, gap=4232, solid=7620203) p=0x80059908
A 987 4232 7620203
987 : 4232 : 0 : 0

OK
asteroid_constitution(as=985, gap=1232, solid=7620203) p=0x80059908
A 985 1232 7620203
985 : 1232 : 0 : 0

OK
asteroid_constitution(as=986, gap=6344, solid=7620203) p=0x80059908
A 986 6344 7620203
986 : 6344 : 0 : 0

OK
The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 4860.0x13d0 exited with code 0]
[Inferior 1 (process 4860) exited normally][/m]

I like Serena · Dec 6, 2014

mathmari said:

I changed something...

Code:

for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p->next != NULL && p->solid != solid){
			p=p->next;
			k=i;
		}
	}
	
p=StarS[k].plasy;
	
printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
                as, gap, solid, p);

This will get you the last star system with at least 1 planetary system.
It will not get you the one with the matching [m]solid[/m] identification. (Doh)

mathmari · Dec 6, 2014

I like Serena said:

This will get you the last star system with at least 1 planetary system.
It will not get you the one with the matching [m]solid[/m] identification. (Doh)

I added a check...

Code:

        int k=-1;
        ...
	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p->next != NULL && p->solid != solid){
			p=p->next;
			k=i;
		}
		if(p->solid == solid){
			k=i;
		}
	}
	if(k == -1){
		return -1;
	}
	
	p=StarS[k].plasy;
	
        printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
                as, gap, solid, p);

Do do we get now the right one?? (Wondering)

I like Serena · Dec 6, 2014

mathmari said:

I added a check...
Do do we get now the right one?? (Wondering)

Let's see... (Thinking)

What if [m]StarS.plasy[/m] is NULL?
Then we can't use [m]p->next[/m]. (Worried)

Code:

p=p->next; k=i;

Aren't you always setting [m]k[/m] here? Even if we did not find [m]solid[/m]? (Wondering)

mathmari · Dec 6, 2014

I like Serena said:
What if [m]StarS.plasy[/m] is NULL?
Then we can't use [m]p->next[/m]. (Worried)

Code:

p=p->next; k=i;

Aren't you always setting [m]k[/m] here? Even if we did not find [m]solid[/m]? (Wondering)

Code:

int k=-1; ... for(i=0; i<Sfreep; i++){ p=StarS[i].plasy; while (p != NULL && p->next != NULL && p->solid != solid){ p=p->next; } if(p->solid == solid){ k=i; } } if(k == -1){ return -1; } p=StarS[k].plasy; printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n", as, gap, solid, p);

Is it better now?? (Wondering)

I like Serena · Dec 6, 2014

mathmari said:

Code:

     int k=-1;
        ...
	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->next != NULL && p->solid != solid){
			p=p->next;
		}
		if(p->solid == solid){
			k=i;
		}
	}
	if(k == -1){
		return -1;
	}
	
	p=StarS[k].plasy;
	
        printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
                as, gap, solid, p);

Is it better now?? (Wondering)

Better yes... but what will happen if some [m]StarS.plasy[/m] is NULL?
I think you'll still have a segmentation fault. (Worried)

Btw, the check [m]p->next != NULL[/m] is redundant, although it does make the logic more complicated. (Nerd)

mathmari · Dec 7, 2014

I like Serena said:

Better yes... but what will happen if some [m]StarS.plasy[/m] is NULL?
I think you'll still have a segmentation fault. (Worried)

If we add [m]p != NULL[/m] in the if statement, would still get a segmentation fault if some [m]StarS.plasy[/m] is NULL?? (Wondering)

Code:

int k=-1; ... for(i=0; i<Sfreep; i++){ p=StarS[i].plasy; while (p != NULL && p->solid != solid){ p=p->next; } if(p != NULL && p->solid == solid){ k=i; } } if(k == -1){ return -1; } p=StarS[k].plasy; printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n", as, gap, solid, p);

I like Serena said:

Btw, the check [m]p->next != NULL[/m] is redundant, although it does make the logic more complicated. (Nerd)

But when we leave the while loop don't we have set a [m]p[/m] [m]p->next[/m] which might be [m]NULL[/m] ?? (Wondering)

I like Serena · Dec 7, 2014

mathmari said:

If we add [m]p != NULL[/m] in the if statement, would still get a segmentation fault if some [m]StarS.plasy[/m] is NULL?? (Wondering)

No, because C short circuits logical expressions.
If [m]p == NULL[/m] the if-condition is considered false without ever evaluating [m]p->solid == solid[/m]. (Nerd)

Code:

int k=-1; ... for(i=0; i<Sfreep; i++){ p=StarS[i].plasy; while (p != NULL && p->solid != solid){ p=p->next; } if(p != NULL && p->solid == solid){ k=i; } } if(k == -1){ return -1; } p=StarS[k].plasy; printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n", as, gap, solid, p);

Much better! (Smile)

But when we leave the while loop don't we have set a [m]p[/m] [m]p->next[/m] which might be [m]NULL[/m] ?? (Wondering)

How so? (Wondering)

Within the while-loop, it is always safe to execute [m]p=p->next[/m], and after the while-loop [m]p[/m] points to the planetary system we're interested in.
What else would we want to do with [m]p->next[/m]? (Thinking)

mathmari · Dec 7, 2014

I like Serena said:

No, because C short circuits logical expressions.
If [m]p == NULL[/m] the if-condition is considered false without ever evaluating [m]p->solid == solid[/m]. (Nerd)

Ahaa... Ok! (Malthe)

I like Serena said:

Much better! (Smile)

(Smile)

I like Serena said:

How so? (Wondering)

Within the while-loop, it is always safe to execute [m]p=p->next[/m], and after the while-loop [m]p[/m] points to the planetary system we're interested in.

I see... (Nerd)

When I add the following at the function

Code:

printf("solid=%p      p->solid==%p \n", solid, p->solid);
	printf("asteroid_constitution(as=%d, gap=%d, solid=%d) p=%p\n",
                as, gap, solid, p);

I get the following: [m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 5100.0x1178]
[New Thread 5100.0x95c]

I OK
C 762
StarSystems = 762
OK
B 7620213 762
PlanetarySystems = 7620213
OK
B 7620203 762
PlanetarySystems = 7620213 7620203
OK
solid=0x74466b p->olsid==0x744675
asteroid_constitution(as=987, gap=4232, solid=7620203) p=0x80059908
A 987 4232 7620203
987 : 4232 : 0 : 0

OK
solid=0x74466b p->solid==0x744675
asteroid_constitution(as=985, gap=1232, solid=7620203) p=0x80059908
A 985 1232 7620203
985 : 1232 : 0 : 0

OK
solid=0x74466b p->solid==0x744675
asteroid_constitution(as=986, gap=6344, solid=7620203) p=0x80059908
A 986 6344 7620203
986 : 6344 : 0 : 0

OK
The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 5100.0x95c exited with code 0]
[Inferior 1 (process 5100) exited normally][/m]

Does this mean that [m]p[/m] still doesn't point to the correct planetary system?? (Wondering)

I like Serena · Dec 7, 2014

mathmari said:

Does this mean that [m]p[/m] still doesn't point to the correct planetary system?? (Wondering)

What do you get if you use:

Code:

int k=-1;
        ...
	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->solid != solid){
			p=p->next;
		}
		if(p != NULL && p->solid == solid){
			k=i;
                        printf("Found in StarS[%d] solid=%d p->solid==%d StarS[k].plasy=%p\n", 
                               k, solid, p->solid, StarS[k].plasy);[/color]
		}
	}
	if(k == -1){
		return -1;
	}
	
	p=StarS[k].plasy;
	
        printf("asteroid_constitution(as=%d, gap=%d, solid=%d) k=%d p=%p\n",
               as, gap, solid, p);[/color]

(Wondering)

mathmari · Dec 7, 2014

I like Serena said:

What do you get if you use:

Code:

int k=-1;
        ...
	for(i=0; i<Sfreep; i++){
		p=StarS[i].plasy;
		while (p != NULL && p->solid != solid){
			p=p->next;
		}
		if(p != NULL && p->solid == solid){
			k=i;
                        printf("Found in StarS[%d] solid=%d p->solid==%d StarS[k].plasy=%p\n", 
                               k, solid, p->solid, StarS[k].plasy);[/color]
		}
	}
	if(k == -1){
		return -1;
	}
	
	p=StarS[k].plasy;
	
        printf("asteroid_constitution(as=%d, gap=%d, solid=%d) k=%d p=%p\n",
               as, gap, solid, p);[/color]

(Wondering)

I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 5248.0x1484]
[New Thread 5248.0x14a8]

I OK
C 762
StarSystems = 762
OK
B 7620213 762
PlanetarySystems = 7620213
OK
B 7620203 762
PlanetarySystems = 7620213 7620203
OK
Found in StarS[0] solid=7620203 p->solid==7620203 StarS[k].plasy=0x80059908
asteroid_constitution(as=987, gap=4232, solid=7620203) p=0x80059908
A 987 4232 7620203
987 : 4232 : 0 : 0

OK
Found in StarS[0] solid=7620203 p->solid==7620203 StarS[k].plasy=0x80059908
asteroid_constitution(as=985, gap=1232, solid=7620203) p=0x80059908
A 985 1232 7620203
985 : 1232 : 0 : 0

OK
Found in StarS[0] solid=7620203 p->solid==7620203 StarS[k].plasy=0x80059908
asteroid_constitution(as=986, gap=6344, solid=7620203) p=0x80059908
A 986 6344 7620203
986 : 6344 : 0 : 0

OK
The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 5248.0x14a8 exited with code 0]
[Inferior 1 (process 5248) exited normally][/m]

I like Serena · Dec 7, 2014

Good! (Happy)

I believe we have confirmed that we're looking at the right star system in the code snippet you provided. (Nod)
That is, the one that matches [m]as[/m], and that contains a planetary system with identification [m]solid[/m].

What's next? (Wondering)

mathmari · Dec 7, 2014

I like Serena said:

Good! (Happy)

I believe we have confirmed that we're looking at the right star system in the code snippet you provided. (Nod)
That is, the one that matches [m]as[/m], and that contains a planetary system with identification [m]solid[/m].

Great! (Mmm)

I like Serena said:

What's next? (Wondering)

So, now the function asteroid_constitution() is correct and we have to find the error at the function destruction(), right?? (Wondering)

I like Serena · Dec 7, 2014

mathmari said:

So, now the function asteroid_constitution() is correct and we have to find the error at the function destruction(), right?? (Wondering)

It appears that way yes. (Thinking)

mathmari · Dec 7, 2014

I like Serena said:

It appears that way yes. (Thinking)

I found out that at the function asteroid_constitution() [m]p->asteroids[/m] is [m]NULL[/m].

I wrote the following, at the end of the function:

Code:

        printf("p->asteroids= %p  \n ", p->asteroids);
        printf("A %d %d %d\n", as, gap, solid);
	while(p->planets != NULL){
			 ...
			  p->asteroids=p->asteroids->next;
	 }
	 printf("p->asteroids= %p  \n ", p->asteroids);

I get the following:

[m]Starting program: /cygdrive/c/cygwin/a.exe file.txt
[New Thread 5260.0x1450]
[New Thread 5260.0x1540]

I OK
C 762
StarSystems = 762
OK
B 7620213 762
PlanetarySystems = 7620213
OK
B 7620203 762
PlanetarySystems = 7620213 7620203
OK
p->asteroids= 0x80059928
A 987 4232 7620203
987 : 4232 : 0 : 0
p->asteroids= 0x0

OK
p->asteroids= 0x80059940
A 985 1232 7620203
985 : 1232 : 0 : 0
p->asteroids= 0x0

OK
p->asteroids= 0x80059958
A 986 6344 7620203
986 : 6344 : 0 : 0
p->asteroids= 0x0

OK
The planetary system doesn't contain any asteroids
D 7620203 5000 failed
[Thread 5260.0x1540 exited with code 0]
[Inferior 1 (process 5260) exited normally][/m]

That means that before the while-loop [m]p->asteroids[/m] is not [m]NULL[/m], but after the while-loop it is [m]NULL[/m]. Why does this occur?? (Wondering)

I like Serena · Dec 7, 2014

mathmari said:
I found out that at the function asteroid_constitution() [m]p->asteroids[/m] is [m]NULL[/m].

I wrote the following, at the end of the function:
Code:
        printf("p->asteroids= %p  \n ", p->asteroids);
        printf("A %d %d %d\n", as, gap, solid);
	while(p->planets != NULL){
			 ...
			  p->asteroids=p->asteroids->next;
	 }
	 printf("p->asteroids= %p  \n ", p->asteroids);

Aha! You found something! (Happy)

That means that before the while-loop [m]p->asteroids[/m] is not [m]NULL[/m], but after the while-loop it is [m]NULL[/m]. Why does this occur?? (Wondering)

Because your changing p->asteroids with [m]p->asteroids=p->asteroids->next;[/m].

I guess you wanted to iterate over the linked list, but you're using the head of the list to do so. Afterwards, that head is not valid any more. Effectively, the linked list is now empty. (Worried)

mathmari · Dec 7, 2014

I like Serena said:

Aha! You found something! (Happy)

(Malthe)

I like Serena said:

Because your changing p->asteroids with [m]p->asteroids=p->asteroids->next;[/m].

I guess you wanted to iterate over the linked list, but you're using the head of the list to do so. Afterwards, that head is not valid any more. Effectively, the linked list is now empty. (Worried)

Yes, I want to iterate over the linked list and print some information.
How can I do it then, without using the head?? (Wondering)

MHB Solve Segmentation Fault: Destroy Planetary System "Solid

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