Question

I have function:

char *zap(char *ar) {

    char pie[100] = "INSERT INTO test (nazwa, liczba) VALUES ('nowy wpis', '";
    char dru[] = "' )";
    strcat(pie, ar);
    strcat(pie, dru);
    return pie;
}

and in main there is:

printf("%s", zap( argv[1] )  );

When compiling I get the warning:

test.c: In function ‘zap’:
test.c:17: warning: function returns address of local variable

How should I return char* propertly?

Answer 1

Your best bet probably is not to return it at all – instead, pass the buffer you want to populate into the function as a parameter.

void zap(char * pie, const char *ar) {
    strcpy( pie, "INSERT INTO test (nazwa, liczba) VALUES ('nowy wpis', '");
    char dru[] = "' )";
    strcat(pie, ar);
    strcat(pie, dru);
}

Then call it like this:

char pie[100];
zap( pie, "foo" );

To bullet proof this function, you also need to pass in the length for the buffer, and then check against this every time you are about to add a new query element.