Returning char * from int function without use of pointer?

Question

I've got a function, that reads from a given file, looks for a given keyword, returning a keyvalue thats seperated by a given string from the word. The return value of my function is char * at the moment, which is subpar for error handling, as far as I understood the whole matter. On the other hand I don't wand to fiddle with a pointer to store the value in. At least in this case.

Is there a way to return the string value through just the function, while returning the int value for success/failure?

My char * code:

#include <stdio.h>  
#include <stdlib.h> 
#include <string.h>

/*!
 * @brief Loads the config file and returns value of requested parameter search
 * @param char *file - Config file to search in
 * @param char *seperator - Seperator to identify keyword and keyvalue 
 * @param char *search - Requested parameter to look for
 * @return char * - Value of found keyword or error if search failed
*/

int confin(char *file, char *seperator, char *search)
{
    FILE *conf;
    char *buffer;
    char *output;
    char line[256];

    char *returnerror = "Error!";


    if((conf = fopen(file, "r")) == NULL)                                   // Try to open file from path, return error if failed
    {
        fprintf(stderr, "Could not open config file \"%s\"!\n", file);
        return returnerror;
    }

    while (fgets(line, sizeof(line), conf) != NULL)                         // Read lines of file until the end is reached
    {
        buffer = strtok(line, seperator);                                   // Search for first appearance of seperator in line;
        if((strcmp(buffer,search)) == 0)                                    // If keyword is found,
        {
            buffer = strtok(NULL, seperator);                               // buffer the keyvalue,
            output = malloc(sizeof(buffer));
            strcpy(output, buffer);                                         // copy it into the output string,
            output[strcspn(output, "\n")] = 0;                              // replace the "\n" char from the end with terminating 0
            fclose(conf);
            return output;                                                  // and return the value of output.        
        }
    }

    fprintf(stderr, "Could not find config keyword \"%s\"!\n", search);
    fclose(conf);
    return returnerror;

}


int main ()
{
    printf("%s\n",confin("test.conf","=","test"));
}

I've tried the following code, yet the returned value is (null)

#include <stdio.h>  
#include <stdlib.h>
#include <string.h>

/*!
 * @brief Loads the config file and returns value of requested parameter search
 * @param char *file - Config file to search in
 * @param char *seperator - Seperator to identify keyword and keyvalue 
 * @param char *search - Requested parameter to look for
 * @return int - 0 on success, 1 on failure 
*/

int confin(char *file, char *seperator, char *search, char *value)
{
    FILE *conf;

    char *output;
    char *buffer;
    char line[256];


    if((conf = fopen(file, "r")) == NULL)                                   // Try to open file from path, return error if failed
    {
        fprintf(stderr, "Could not open config file \"%s\"!\n", file);
        return 1;
    }

    while (fgets(line, sizeof(line), conf) != NULL)                         // Read lines of file until the end is reached
    {
        buffer = strtok(line, seperator);                                   // Search for first appearance of seperator in line;
        if((strcmp(buffer,search)) == 0)                                    // If keyword is found,
        {
            buffer = strtok(NULL, seperator);                               // buffer the keyvalue,
            output = malloc(sizeof(buffer));
            strcpy(output, buffer);                                         // copy it into the output string,
            output[strcspn(output, "\n")] = 0;                              // replace the "\n" char from the end with terminating 0.
            strcpy(value,output);                                           // Store the new value in my return value     
            fclose(conf);
            free (output);
            return 0;                                                       // and return the value of output.        
        }
    }

    fprintf(stderr, "Could not find config keyword \"%s\"!\n", search);
    fclose(conf);
    return 1;

}


int main ()
{
    char value[256] = "\0";
    printf("%s\n",confin("test.conf","=","test",value));
}

Hope this matter is sorted out quick. Even if it means I DO have to use the pointer method at the end. Thanks in advance!

One way is to make a structure containing both a char* and an int; then make your function return that. It is common practice in C, however to just pass a char** as a return parameter if you want to return a char*. — merlin2011
Another way in C could be to return the char* outcome in a pointer that is passed when the function is called. The return value of the function would then be an int to indicate if it succeeded or not. — EmbedWise
My recommendation would be to use some printf statements in you function to trace what is happening. C can be funny when it comes to many of its standard library functions. They may not work as you think they do. — FernandoZ
Returning NULL when you don't find a string value seems reasonable. Also, output = malloc(sizeof(buffer)); just allocates 4 or 8 bytes (the size of a pointer). — Bo Persson

Rogus Rogus · Accepted Answer · 2017-04-21T07:32:57

Change:

int main ()
{
    char value[256] = "\0";
    printf("%s\n",confin("test.conf","=","test",value));
}

to:

int main ()
{
    char value[256] = "\0";
    int retval = confin("test.conf","=","test",value);
    if(retval)
        // some error handling
    printf("%s\n", value);
}

What you did was call confin, which assigned the string value to value, but you tried to print the returned int from this function (as a string) instead of value.

You could also just return char* and in case of the key not being present in your config file return NULL. This is an easy case just for "No such key" type error. In such a case you'd just have to check if confin returned NULL.

Returning char * from int function without use of pointer?

2 Answers