CODEWITHSUNDEEP
crealloc
vanderer
vanderer

Reputation: 13

reallocing array of structs

so I have spent some hours trying to figure out why my realloc doesnt enlarge my array of structs, but I seem to make no progress. Realloc either fails or doesnt enlarge the array. Is there any obvious mistake that Im making?

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


typedef struct fileInfo {
    char accessRights[12];
    short hardLinks;
    short userName;
    short groupName;
    long size;
    char *time;
    char *fileName;
    short nrOfNode;
} fileInfo;


void enlargeFileInfos(fileInfo *fileInfoArray, int currentSize)
{
    fileInfo *temp = (fileInfo*)realloc(fileInfoArray, (currentSize + 1) * sizeof(fileInfo));
    if (!temp) {
        printf("realloc --FAILED--\n");
        return;
    }
    fileInfoArray = temp;
    printf("fileInfo grew to %d item(s)\n", currentSize + 1);
}

int main( )
{
    size_t nrOfDirs = 1;
    fileInfo *fileInfoArr = malloc(sizeof(fileInfo));

    for (int i = 0; i < 5; i++) {
        enlargeFileInfos(fileInfoArr, nrOfDirs);
        nrOfDirs++;
    }
    return 0;
}

Upvotes: 1

Views: 65

Answers (1)

medalib
medalib

Reputation: 937

To realloc memory on which fileInfoArray points to inside enlargeFileInfos, you have to pass its address to the function:

void enlargeFileInfos(fileInfo **fileInfoArray, int currentSize)
{
    fileInfo *temp = realloc(*fileInfoArray, (currentSize + 1) * sizeof(fileInfo));
    if (temp == NULL) {
        printf("realloc --FAILED--\n");
        return;
    }
    *fileInfoArray = temp;
    printf("fileInfo grew to %d item(s)\n", currentSize + 1);
}

Then you call the function in this way:

enlargeFileInfos(&fileInfoArr, nrOfDirs);

As pointed by Jonathan Leffler in comments, an alternative way is to return the realloced memory from the function enlargeFileInfos:

fileInfo *enlargeFileInfos(fileInfo *fileInfoArray, int currentSize)
{
    fileInfo *temp = realloc(fileInfoArray, (currentSize + 1) * sizeof(fileInfo));
    if (temp == NULL) {
        printf("realloc --FAILED--\n");
        return NULL;
    }
    printf("fileInfo grew to %d item(s)\n", currentSize + 1);
    return temp;
}

And than, you use it this way:

fileInfoArr = enlargeFileInfos(fileInfoArr, nrOfDirs);
if (fileInfoArr == NULL) {
    /* Handle allocation failure */    
}

And after you finish working with fileInfoArr, don't forget to free it:

free(fileInfoArr);

I have removed the cast from realloc, so take a look on Do I cast the result of malloc?, and change the signature of main to int main(void) .

Upvotes: 1

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