C - Read file byte by byte using fread

Question

I am trying to read a file byte by byte (this is important because I have to measure performance). I can't seem to get the fread to work properly. Right now it just gives me the last byte of the file.

This is what I have:

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

int main(int argc, char **argv) { 
    FILE *fileptr;
    char *buffer;
    long filelen;
    int i;

    fileptr = fopen(argv[1], "rb");         
    fseek(fileptr, 0, SEEK_END);          
    filelen = ftell(fileptr);            
    rewind(fileptr);                      
    buffer = (char *)malloc((filelen+1)*sizeof(char)); 

    for(i = 0; i < filelen; i++) {
       fread(*&buffer, 1, 1, fileptr); 
    }

    printf("File len: %ld\n", filelen);
    printf("%s\n",*&buffer);

    fclose(fileptr); // Close the file

    return 0;
}

Any help is appreciated

The os is going to buffer stuff, so measuring performance like this is not very meaningfull — OldProgrammer
– OldProgrammer, Commented Feb 2, 2015 at 1:37
Also, *&buffer is actually the same as buffer or &buffer[0]. This is because & takes the address of the variable buffer, creating a pointer of type char**, then * dereferences that pointer, turning it back into the same char* that we started from, aka buffer. — RudolfW
– RudolfW, Commented Feb 2, 2015 at 1:38
@OldProgrammer What would be a good way? I just need to measure how long it takes to read the file. — ChaniLastnamé
– ChaniLastnamé, Commented Feb 2, 2015 at 1:39
If you're reading one byte at a time, just use getc instead of fread. fread is defined to work as if by repeated calls to getc or fgetc anyway. — Keith Thompson
– Keith Thompson, Commented Feb 2, 2015 at 1:51
@paxdiablo: I did not say *&buffer was wrong, I just said it was about as meaningful as *&*&*&*&*&*&*&buffer of buffer+1-1. :) — RudolfW
– RudolfW, Commented Feb 2, 2015 at 1:56

Yellows · Accepted Answer · 2015-02-02 01:47:28Z

7

You need to advance the pointer:

for(i = 0; i < filelen; i++) {
       fread(buffer+i, 1, 1, fileptr); 
}

Currently, at every iteration the loop overwrites the previous character. No surprise then that only the last character appears.

By the way, you should add a '\0' character after the loop, which will mark the end of the string, so that printf() will stop printing after it.

edited Feb 2, 2015 at 1:47

answered Feb 2, 2015 at 1:35

Yellows

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