Question

Possible Duplicate:
Is it a good idea to return “ const char * ” from a function?
how to return char array in c++?

What is wrong with this return? I’m trying to return the current path using the following function but it doesn’t seems to be correct:

Please Not: I need an char return not string.

char* getINIfile(void)
{
    char buffer[MAX_PATH];
    GetModuleFileName( NULL, buffer, MAX_PATH );
    string::size_type pos = string( buffer ).find_last_of( "\\/" );
    string path = string( buffer ).substr( 0, pos) + "\\setup.ini";

    char *ini_local= (char*)path.c_str();

    printf(ini_local); // so far output OK!

    return ini_local;
}

main
{
    printf(getINIfile()); // output Not OK! 

    char mybuffer[200];
    GetPrivateProfileStringA( "files","DLL","0",  mybuffer,200, getINIfile());
    printf(mybuffer);

}

Answer 1

You’re returning an address that goes out of scope when the function exits, and so it’s no longer valid: std::string path is local to the function getINIFile and so it’s invalid after the function exits, as is the address that you get from path.c_str().

In this case you can just return the std::string from your function. If you really need a C string later, you can use c_str() then:

std::string getINIfile(void)
{
    //...

    return path;
}


int main()
{
    string path = getINIFile();

    // do something with path.c_str():
    const char *cPath = path.c_str();
}

Given your code I can’t think of any reason that you must have a char* return, but if so you’ll need to allocate a buffer on the heap:

char *getINIfile(void)
{
    char *buffer[MAX_PATH];
    GetModuleFileName(NULL, buffer, MAX_PATH);
    string::size_type pos = string(buffer).find_last_of( "\\/" );
    string path = string(buffer).substr( 0, pos) + "\\setup.ini";

    char *ini_local = new[path.size()];
    strncpy(ini_local, path.c_str(), path.size());

    printf(ini_local); // so far output OK!

    return ini_local;
}

But this is a really awful mix of standard C strings and std::string: just using string to manipulate the path and passing around char* everywhere else.

Using only standard C, replacing find_last_of with strrchr – note the lack of error handling:

char *getINIfile(void)
{
    char *buffer = new[MAX_PATH];
    char *pos = NULL;
    char *ini_local = NULL;

    GetModuleFileName(NULL, buffer, MAX_PATH);
    pos = strrchr(buffer, "\\/");
    // check for and handle pos == NULL

    buffer[pos] = '\0';

    strncat(buffer, "\\setup.ini", MAX_PATH - strlen(buffer));

    printf(buffer);

    return buffer;
}