Exception writing data into a new file

Question

My task is to read a yuv file and to each component(Y,Cb,Cr) of it, I'm appending some data and storing it into another file. I have tried the below code:

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

void main()
{
    FILE *fp=fopen("traffic_1920x1080.yuv","rb");
    FILE *myYUV=fopen("traffic_1920x1088.yuv","ab");
    int count=0;
    unsigned char *y=(unsigned char*)malloc(sizeof(unsigned char)*1920*1080);
    unsigned char *u=(unsigned char*)malloc(sizeof(unsigned char)*(1920/2)*(1080/2));
    unsigned char *v=(unsigned char*)malloc(sizeof(unsigned char)*(1920/2)*(1080/2));

    unsigned char ypad[1920*8];
    unsigned char upad[(1920/2)*4];
    unsigned char vpad[(1920/2)*4];

    for(int i=0;i<(1920/2)*4;i++)
    {
        ypad[i]=255;
        upad[i]=128;
        vpad[i]=128;
    }
    for(int i=(1920/2)*4;i<1920*8;i++)
        ypad[i]=255;
    while (!feof(fp))
    {
        fread(y,sizeof(unsigned char),1920*1080,fp);
        fread(u,sizeof(unsigned char),1920/2*1080/2,fp);
        fread(v,sizeof(unsigned char),1920/2*1080/2,fp);

        fwrite(y, sizeof(unsigned char),1920*1080,myYUV);
        fwrite(ypad,sizeof(unsigned char),1920*8,myYUV);

        fwrite(u,sizeof(unsigned char),1920/2*1080/2,myYUV);
        fwrite(upad,sizeof(unsigned char),1920/2*4,myYUV);

        fwrite(v,sizeof(unsigned char),1920/2*1080/2,myYUV);
        fwrite(vpad,sizeof(unsigned char),1920/2*4,myYUV);

        printf("Frame %d created\r",count);
        y+=1920*1080;
        u+=1920/2*1080/2;
        v+=1920/2*1080/2;
        count ++;
    }
    free(y);
    free(u);
    free(v);

    fclose(fp);
    fclose(myYUV);
}

Howevr the above code works fine for the first loop, but in the second loop i get an exception

Access violation writing location 0x0092f000.

at line fwrite(y, sizeof(unsigned char),1920*1080,myYUV);

Is this a problem in pointer increment? or it is something else? Please reply. Thanks in advance.

Answer 1

These increments:

y+=1920*1080;
u+=1920/2*1080/2;
v+=1920/2*1080/2;

will increment the pointers past the end of the allocated memory. For example, y points to the start of 1920*1080 bytes of allocated memory. Increasing it by that much makes it point past the end of that memory. This results in reading/writing to/from unallocated memory. That's why you get an access violation.

I don't actually see a reason for those pointers to be incremented at all.

Other than that, your code should check for error conditions (did fopen() succeed, etc.)