Solving Error in `./recover': free(): invalid next size (normal): 0x0000000001ddd270 *** Aborted in c

Question

Code must read 512 bytes at a time from a file that has raw JPEGs in order to retrieve them. When a JPEG is found, all the following blocks of 512 bytes are stored in a a file until a new JPEG is found, once a new JPEG is found, the file img is closed and then opened as new to store a new image. The code runs fine if I comment or erase the fclose(img); line, othwerwise it shows the error above.

Here's the code

#include <stdio.h>
#include <cs50.h>
#include <stdlib.h>


int main (int argc, char *argv[]){

if(argc != 2){

    fprintf(stderr, "Usage: ./recovery image\n");
    return 1;

}

FILE *card = fopen(argv[1], "r");

if (card == NULL){

    fprintf(stderr, "Cannot open image\n");
    return 2;

}

FILE *buffer1 = malloc(sizeof(card));

int n = 0;
int picsNum = 0;

while(fread(buffer1, 512, 1, card)){

    n ++;

}

//printf("%i", n);

bool foundJPEG = false;
int j = 0;
bool fstJPEG = false;
FILE *img = NULL;
int counter = 0;

fseek(card, 0, SEEK_SET);

for(int i = 0; i < n; i++){


    unsigned char fst;
    unsigned char snd;
    unsigned char thrd;
    unsigned char fth;
    unsigned char buffer2[508];

    fread(&fst, 1, 1, card);
    fread(&snd, 1, 1, card);
    fread(&thrd, 1, 1, card);
    fread(&fth, 1, 1, card);
    fread(buffer2, 508, 1, card);
    //printf("%i,%i,%i,%i,", fst, snd, thrd, fth);

    if(fst == 0xff && snd == 0xd8 && thrd == 0xff && (fth & 0xf0) == 0xe0){

        printf("Found\n");

        if(fstJPEG){

            fclose(img);

        }

        printf("%i,%i,%i,%i,", fst, snd, thrd, fth);
        foundJPEG = true;
        picsNum++;
        fstJPEG = true;

        char JPEG[8];
        sprintf(JPEG, "%03i.jpg", j);
        j++;
        img = fopen(JPEG, "w");

    } else {

        foundJPEG = false;

    }

    if(fstJPEG){

        fwrite(&fst, 1, 1, card);
        fwrite(&snd, 1, 1, card);
        fwrite(&thrd, 1, 1, card);
        fwrite(&fth, 1, 1, card);
        fwrite(buffer2, 508, 1, card);
        counter++;
        printf("%i,", counter);

    }

}    

fclose(card);    
printf("%i,\n", picsNum);

}

This `malloc(sizeof(card));` allocates space for a single pointer (4 or 8 bytes), not the 512 bytes needed for `fread`. Also `buffer1` should likely be `char*`and not `FILE*`. — Bo Persson, Aug 14 '17 at 22:56
`FILE *buffer1 = malloc(sizeof(card));` : this doesn't make sense. — BLUEPIXY, Aug 14 '17 at 22:56

score 0 · Answer 1 · answered Aug 14 '17 at 22:57

0

This is wrong in multiple ways:

FILE *buffer1 = malloc(sizeof(card));

First of all, card is FILE *, so this allocates a pointer, not a FILE. Second of all, you can't open a file this way. You must use fopen() or something similar.

answered Aug 14 '17 at 22:57

Dietrich Epp

205,541
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@pm100: Well, I don't know if the asker wants to open another file or allocate a buffer. – Dietrich Epp Aug 14 '17 at 23:02
I changed FILE to char in that line, the program is now fixed, thand – gerry.ascencio Aug 16 '17 at 00:25

score 0 · Accepted Answer · answered Aug 14 '17 at 22:58

0

what do you think

FILE *buffer1 = malloc(sizeof(card));

is doing? It is actually creating a buffer that is 4 or 8 bytes long. (the size of a FILE * ). YOu are told to read 512 bytes at once. And its a char * buffer not a FILE *. How about doing.

char *buffer1 = malloc(512);

answered Aug 14 '17 at 22:58

pm100

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This seems to have fixed the issue. However, the program outputs files that are in a format other thatn JPEG, do you know why this might be? – gerry.ascencio Aug 16 '17 at 00:14
I just realized I was writing back into card instead to into img, thats why the output was weird – gerry.ascencio Aug 16 '17 at 00:25

Solving Error in `./recover': free(): invalid next size (normal): 0x0000000001ddd270 *** Aborted in c

2 Answers2