CODEWITHSUNDEEP
c
Fendrix
Fendrix

Reputation: 566

Returning char pointer to a different files

Is it possible to return a char Pointer even the calling function is not in the same file.... if I call the function for example:

 void gotest(sqlite3 *pt,char *nutzers)
{
    char string[1064];
    char *text;
    text = get_data_byName(pt,"whatever",string);   
    printf("test %s \n\n\n same file",text);    
}

 char *get_data_byName(sqlite3 *ptr,char *user,char *resulter)
{
    .......
    resulter = "TestCall";
    return resulter;
}

if gotest(sqlite3 *pt,char *nutzers) and char *get_data_byName(sqlite3 *ptr,char *user,char *resulter) are in different files then gcc gives the following

Assignment makes pointer from integer without a cast

if I have both functions in one file everything works fine.

compiling like:

gcc -o test test.c time.c database.c libircclient-1.6/src/libircclient.o -lsqlite3

Upvotes: 2

Views: 372

Answers (5)

Linuxios
Linuxios

Reputation: 35788

You need headers for your files. If GCC doesn't see a function prototype in the file it's used in, GCC assumes that the function returns an int. You need to read up on headers. In the mean time, putting this in the file where you use get_data_byName will be enough:

char *get_data_byName(sqlite3 *ptr,char *user,char *resulter);

You have to remember that although when GCC is linking, it knows that you define get_data_byName, when it's compiling, it needs to know what parameters and return values it has. That's the purpose of a header. Headers contain function prototypes. A function prototype looks like this:

char *get_data_byName(sqlite3 *ptr,char *user,char *resulter);

If you put the prototypes of all of the functions defined in one .c file in one .h file, and them #include that header in the files that use the function, you wont get that error anymore. So if you have a file called get_data_by_name.c, this would be get_data_by_name.h:

#ifndef GET_DATA_BY_NAME_H
#define GET_DATA_BY_NAME_H
char *get_data_byName(sqlite3 *ptr,char *user,char *resulter);
#endif

Then just #include it in the file that uses get_data_byName:

#include "get_data_by_name.h"

Upvotes: 2

Eudis Duran
Eudis Duran

Reputation: 782

Depends how you have them "in separate files." The format specified in K&R would require 2 extra .h files for each .c file you have. The .h files would declare the function prototypes. From there, you can include the file_2.h into your file_1.c, and make get_data_byName available to gotest. Hope that helps.

**file_1.c**
include "file_1.h"
include "file_2.h"

void gotest(sqlite3 *pt,char *nutzers)
{
    char string[1064];
    char *text;
    text = get_data_byName(pt,"whatever",string);   
    printf("test %s \n\n\n same file",text);    
}


**file_2.c**
char *get_data_byName(sqlite3 *ptr,char *user,char *resulter)
{
    .......
    resulter = "TestCall";
    return resulter;
} 

**file_1.h**
void gotest(sqlite3 *pt,char *nutzers);

**file_2.h**
char *get_data_byName(sqlite3 *ptr,char *user,char *resulter);

Upvotes: 2

unwind
unwind

Reputation: 400069

Yes, it's certainly possible. You need to have a declaration of the function before calling it:

char * get_data_byName(sqlite3 *ptr, char *user, char *resulter);

Also, you should really use const for pointers where applicable.

And remember that if you need to return a non-literal string, you need to think about memory management.

Upvotes: 2

hmjd
hmjd

Reputation: 122001

There must be no declaration of get_data_byName() visible to gotest(), so the compiler generates an implicit declaration and assigns a return type of int, hence the warning. To resolve add a declaration for get_data_byName(), in a header file for example, and ensure it is visible to gotest().

get_data.h:

#ifndef GET_DATA_HEADER_H_
#define GET_DATA_HEADER_H_

extern char* get_data_byName(sqlite3 *ptr,char *user,char *resulter);

#endif

Then #include <get_data.h> in the .c file where gotest() is defined.

Upvotes: 2

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726987

You get the error not because the functions are in different files: it is perfectly fine for functions from different compilation units to call each other. The real problem is that you are trying to call a function from the other file without providing a prototype. When this happens, C assumes a return type of int.

Make a header file with this content:

get_data_byName.h

char *get_data_byName(sqlite3 *ptr,char *user,char *resulter);

Now include this header file in both of your C files:

#include "get_data_byName.h"

The compilation warning will go away.

Upvotes: 2

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