Question

Please tell me where I am going wrong.

I have a file which I need to copy last n bytes to an array.

    char *buffer = (char *)malloc(sizeof(char)*n);
    size_t result = fread(buffer,sizeof(char)*n,1,outptr);

The value of result is 0.

Everything up till here in my code works right( I have checked all the values with gdb). I am freeing the buffer too after some lines.

n is userinputted. The output ptr is used as

    FILE *outptr = fopen(outfile,"w") 

//The outfile name is also user inputted and is checked to make sure it is a bmp file.

Answer 1

You are attempting to read from a file you have opened in write mode.

Change:

FILE *outptr = fopen(outfile,"w");

to:

FILE *outptr = fopen(outfile,"r"); /* Use "rb", not "r", if 'outfile' is binary. */