return char array function error [duplicate] - c++

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Closed 10 years ago.
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

path goes out of scope at the end of the function and you are returning an internal pointer in that out of scope object. try returning an std::string instead
std::string 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 path;
}

Answer 2

You're returning an address that goes out of scope when the function exits, and so it's no longer valid: std::string path is local to the function getINIFile and so it's invalid after the function exits, as is the address that you get from path.c_str().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

Answer 3

The function is returning a pointer to a local variable, which goes out of scope, leaving you with a dangling pointer. Why not just return an std::string by value?
std::string getINIfile() {
....
return path;
}
Then you can just use the string's underlying char* on the caller side:
const std::string s = getINIfile();
const char* c = s.c_str();