The discussion revolves around the manipulation of strings in C++, specifically the process of copying the content of a C++ string into a C-string while managing memory allocation correctly. Participants explore issues related to Visual Studio (VS) and the differences between C-strings and character arrays.
Participants do not reach a consensus on the original question regarding C-string manipulation. There are multiple competing views on the functionality of the program and the issues faced in Visual Studio, with some participants successfully running the code while others encounter errors.
Participants mention specific error messages and behaviors in Visual Studio, indicating potential issues with permissions and project settings that are not resolved within the discussion. The distinction between C-strings and character arrays is also highlighted, but not fully explored.
This discussion may be useful for C++ programmers dealing with string manipulation, memory management, and those encountering issues with Visual Studio or seeking clarification on C-strings versus character arrays.
Just to be clear, str2 has 4 bytes allocated, but its length, as determined by strlen() would be 3.jtbell said:
#include <iostream>
#include <iomanip>
using namespace std;
//--------------------------------------------------------------------------
// Display the contents of a char array as 2-digit hexadecimal numbers, etc.
void DisplayHex (char carray[], int size)
{
cout << "as hex: ";
for (int k = 0; k < size; ++k)
{
cout << hex << setfill('0') << setw(2) << (int)carray[k] << " ";
}
cout << endl;
cout << "as C-string: " << carray << endl;
cout << "sizeof = " << size << endl;
cout << "strlen = " << strlen(carray) << endl;
}
//--------------------------------------------------------------------------
int main ()
{
char animal[] = {'c', 'a', 't', '\0'};
cout << "\nChar array #1: c a t \\0" << endl;
DisplayHex (animal, sizeof(animal));
char animals[] = {'c', 'a', 't', '\0', 'd', 'o', 'g'};
cout << "\nChar array #2: c a t \\0 d o g" << endl;
DisplayHex (animals, sizeof(animals));
cout << endl;
return 0;
}Char array #1: c a t \0
as hex: 63 61 74 00
as C-string: cat
sizeof = 4
strlen = 3
Char array #2: c a t \0 d o g
as hex: 63 61 74 00 64 6f 67
as C-string: cat
sizeof = 7
strlen = 3My oh my, how apropos!yungman said:
What do you mean? I have been thanking everyone that help me all the time. Read my past posts. I can't say enough thanks to Mark and Jarvis lately for all the help.Tom.G said:
I have been reviewing pointers again as I have to use them in exercise of Class objects. I thought I understand very well...until I really get down and step by step looking at the address and content in it in Debug. Have I learn more. I have no question, just want to say the pointers is still the hardest subject so far in C++ for me. I actually re-write this part of my notes and use a working program with Immediate Window to show step by step using break points to show the address and content how the pointers work. I attached that page of my notes. I really got into it this time.Tom.G said:
yungman said:
yungman said:
Did you read, I said lately. I thank everyone that help me.Vanadium 50 said:
Yes! As they say, "Practice makes perfect."yungman said:
Thanks you for the encouragement. I needed that. Particularly I was tripped up by the algebra question from my little grand daughter. She's only freshman in high school! We Chinese called this the old cat got its whiskers burned.Tom.G said:
Thanks. Why is that so? I know I read from Mark also, but the books keep using it. I know I need to type std::count <<...; every time if I don't use namespace std. I was wondering why my invItem.h need it. I don't have cin or count:Jarvis323 said:
#ifndef invItem_H
#define invItem_H
#include <cstring>
#include <string>
using namespace std;
class invItem
{
private:
string* description;
double cost;
int units;
public:
//Constructor. pointer desc points to C-string, c for cost, u for units.
invItem(string** desc, double c, int u)
{
string St2 = **desc;//St2 = St1 in main.
int length = St2.length();
description = new string[length];//allocate new memory using pointer description.
*description = St2;//copy the description to memory
*desc = description;
cost = c; units = u;
}Like I said, it's usually fine in a cpp file, but should be avoided in .h files.yungman said:
Thank you, no wonder I got error lining up on me! I only know cin and count!Jarvis323 said:
You are missing the point that was discussed about 500 posts ago in a different thread that the ease of use of the Standard Template Library (STL) classes comes with three penalties:yungman said:
Thanks so much for the reply. I did not know that. I don't recall I ever ask this question. I don't even know enough to ask.pbuk said:
These are almost the same, with the only difference being that a C-string is a null-terminated array of type char, and a char array is just an array of type char.yungman said:
The line with "#include <cstring>" should be deleted. The code shown doesn't use any C-strings.yungman said:
There's a big difference between C-strings (i.e., null terminated character arrays) and the standard template library (STL) string template class. C-strings are so called because this is how strings were implemented in C, before C++ came on the scene.yungman said:
When you pass a C-string to a function, what's being passed is a pointer to the first character of the string. If your function is intended to modify a C-string parameter, you'll run into problems if the function tries to insert more characters than the C-string had allocated to it.yungman said:
#include <cstring> // For strcpy_s()
#include <iostream>
using std::count;
using std::endl;
void modifyStr(char * str);
int main()
{
char Str[10] = "dogs";
count << "Before modification: " << Str << endl;
modifyStr(Str);
count << "After modification: " << Str << endl;
}
void modifyStr(char * str)
{
strcpy_s(str, sizeof("hot dogs"), "hot dogs");
}An STD string object will generally take up more space in memory, I believe, because in addition to the memory used to store the characters in the string, there is also memory set aside in reserve, in case you append some more characters to the string.yungman said:
Mark44 said:
We're just talking about a few bytes, say 20 to 30, so it's not like a massive hit on memory.yungman said:
Ah, it's time for me to get more familiar with c-string anyway, what is an extra day or so.Mark44 said:
Yes, good catch. What I was talking about was actually heap fragmentation, but the effect on a microcontroller is much the same.Jarvis323 said:
Ha ha, You ruin my day!pbuk said:
string firstName, lastName;
count << "Enter your first name: ";
cin >> firstName;
count << "Enter your last name: ";
cin >> lastName;
string fullName = firstName + " " + lastName;