CODEWITHSUNDEEP
cpointersfread
kevin
kevin

Reputation: 173

reading a portion of file to a buffer using fread

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.

Upvotes: 0

Views: 453

Answers (2)

hmjd
hmjd

Reputation: 121961

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. */

Upvotes: 1

Sangeeth Saravanaraj
Sangeeth Saravanaraj

Reputation: 16597

size_t result = fread(buffer, n, 1, outptr); should fine.

OTOH, is the file that you're working on is empty?

Please make sure that fopen() was successful and also check whether malloc() was successful!

On a completely different note, sizeof() and fread() returns size_t and that should be cast to int.

Upvotes: 1

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