asked on

return a string from a dll function

I have a visual c++ (version 6) DLL that takes a parameter username, determines the date and time, stores this datetime value in a database.

I must now return this datetime(String) back to the calling program and I am not sure how to do it.

The dll function is defined as:

__declspec(dllexport) int _cdecl StoreToken(char *strContextName) {
time_t ltime;
struct tm *gmTime;
char *currentUTC;

time( &ltime );
gmTime = gmtime( &ltime );
currentUTC = strdup(asctime(gmTime));
//Code to store currentUTC in database has been omited
//currentUTC is what I would like to return to the
//calling program
...
return bstored; // I am using this to determine is the
// function worked.
}

The test program I am using is as follows:

// TestDll.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

extern int StoreToken(char *contextName);

int main(int argc, char* argv[])
{
char thedate[] = "";
char contextname[] = ".cn=sdbanks.ou=itd.ou=chho.o=apm";
StoreToken(contextname);
return (0);
}

What changes must I do to return currentUTC to the calling program.

jkr

Make it read

__declspec(dllexport) int _cdecl StoreToken(char *strContextName, char* pszUTCBuf, long lnBufSize) {
time_t ltime;
struct tm *gmTime;
char *currentUTC;

time( &ltime );
gmTime = gmtime( &ltime );
currentUTC = strdup(asctime(gmTime));

if ( strlen ( currentUTC) < lnBufSize) {

strcpy ( pszUTCBuf, currentUTC);

} else {

// buffer not big enough, error!
}

return bstored; // I am using this to determine is the
// function worked.
}

#define MAX_THEDATE 256
int main(int argc, char* argv[])
{
char thedate[ MAX_THEDATE] = "";
char contextname[] = ".cn=sdbanks.ou=itd.ou=chho.o=apm";
StoreToken(contextname, thedate, MAX_THEDATE);
return (0);
}

ASKER CERTIFIED SOLUTION

jkr

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sdbanks

ASKER

Thank you very much. It worked great. I was looking all day for information on how to do this.

jkr

You're welcome - that's the way that e.g. your app receives textual information from Windows (see e.g. 'GetWindowsDirectory()'). Just one correction that I'd recommend:

__declspec(dllexport) int _cdecl StoreToken(char *strContextName, char* pszUTCBuf, long lnBufSize) {
time_t ltime;
struct tm *gmTime;
char *currentUTC;

time( &ltime );
gmTime = gmtime( &ltime );
currentUTC = strdup(asctime(gmTime));

if ( strlen ( currentUTC) < lnBufSize) {

strcpy ( pszUTCBuf, currentUTC);

} else {

// buffer not big enough, error!
}

free ( currentUTC); // <----!!! will cause memory leaks otherwise!

return bstored; // I am using this to determine is the
// function worked.
}

sdbanks

ASKER

I will do that right away. Is that something I should do for every variable when I exit the routine or just for char *currentUTC?

jkr

Well, in this case, just that variable. It is because "strdup()" uses a "malloc()" to return the duplicated string, and the docs also say that you have to "free()" it manually...