assignment makes pointer from integer without a cast, in C when returning pointer

Question

I'm coded function which splits 2 char arrays and integer into one string and returns pointer to new char array, but when compiling I'm getting this warning:

warning: assignment makes pointer from integer without a cast

mapfile = world_to_char( "maps/", map, ".bin" );

^

Here is my code, first two are lines from file where gcc is giving warning to me:

char *mapfile;
mapfile = world_to_char( "maps/", map, ".bin" );

and function (I know that it works only with numbers from [0;99], but it's enough for me):

char *world_to_char( char dir[], int number, char ext[] ) {
    char id[ 3 ] = { 0, 0, 0 };

    if( number > 9 ) {
        id[ 1 ] = ( number % 10 ) + '0';
        number /= 10;
    }
    id[ 0 ] = number + '0';

    char *map;
    map = malloc( MAX_MAP_FILENAME * sizeof( char ) );

    strcpy( map, dir );
    strcat( map, id );
    strcat( map, ext );

    return map;
}

Why I'm getting this warning? I'm returning pointer not integer.

Questions seeking debugging help ("why isn't this code working?") must include the desired behavior, a specific problem or error and the shortest code necessary to reproduce it in the question itself. Questions without a clear problem statement are not useful to other readers. See: How to create a Minimal, Complete, and Verifiable example. — too honest for this site
– too honest for this site, Commented Jan 8, 2016 at 22:15
If you're using a C99 compiler, you should be getting warnings about calling a function that was not previously declared. If you're not using a C99 or later compiler, or you're not getting the warnings, find the options that give you the warning. If you're using GCC, consider using options as stringent as gcc -O3 -g -std=c11 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes -Wold-style-definition -Werror. You can be more stringent if you like. — Jonathan Leffler
– Jonathan Leffler, Commented Jan 9, 2016 at 7:26

Iharob Al Asimi · Accepted Answer · 2016-01-08 22:06:07Z

3

It's likely that world_to_char() is defined after main(), add a function prototype and it should work. So before main() add this

char *world_to_char(char *dir, int number, char *ext);

the parameters with "java" style char dir[] will become pointers anyway, so let's make it clear by changing them to char *dir instead.

The error message is because of implicit declaration, since the compiler haven't seen a declaration when you call the function it assumes that it returns int, so assigning int to char * is making a pointer from an integer without a cast.

edited Jan 8, 2016 at 22:06

answered Jan 8, 2016 at 22:04

Iharob Al Asimi

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2 Comments

Kerrek SB Over a year ago

A declaration would suffice: char *world_to_char(); :-)

Iharob Al Asimi Over a year ago

@Szeldon It's a common mistake, your question was really well written and formatted.

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