segmentation fault on strcat

[markman]

I have this code:

#include <string>
#include <iostream>
using namespace std;

void main() {
    char* sztest = "hello";
    char* retVal = "";
    retVal = strcat(retVal,sztest);
    cout << retVal << endl;
}

Compiling using 'g++ test.cpp'

I run it and get segmentation fault that comes from the strcat.

Now whats wrong with this code?

[Zaei]

Its retVal.

#include <string>
#include <iostream>
using namespace std;

void main() {
    char* sztest = "hello";
    char* retVal = new char[128];
    retVal[0] = 0;
    retVal = strcat(retVal,sztest);
    cout << retVal << endl;
    delete retVal;
}

strcat was attempting to write past the end of retVal, which was 1 byte long. Bad idea =).

Z.

[parksie]

#include <string>
#include <iostream>
using namespace std;

void main() {
    char* sztest = "hello";
    char* retVal = "";
    retVal = strcat(retVal,sztest);
    cout << retVal << endl;
}

What you have here is two pointer values, pointing at two separate, fixed-size, unmodifiable strings. The compiler should give a warning that they need to be const char*. Try the -Wall switch to g++.

Anyway, in C++ what you should do is:

#include <string>
#include <iostream>
using namespace std;

void main() {
    string test("Hello");
    string retVal("World");

    test += " ";
    test = test + retVal;
    cout << test << endl;
}

...or something similar using the string class

[markman]

thanks but now how do I change it back to a char* so I can return it?
return (char*)test;
^doesnt work^

[parksie]

You can't return a pointer, at least you shouldn't. It's a memory leak, or may point to no-longer-allocated memory.

What are you trying to do?

[markman]

I have a class that uses char*'s throughout it, and I want to use strings in the rest. Can I convert from string to char*?

[Zaei]

std::string::c_str() returns a const char*.

Z.