C file read leaves garbage characters

Question

Hi. I'm trying to read the contents of a file into my program but I keep occasionally getting garbage characters at the end of the buffers. I haven't been using C a lot (rather I've been using C++) but I assume it has something to do with streams. I don't really know what to do though. I'm using MinGW.

Here is the code (this gives me garbage at the end of the second read):

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

char* filetobuf(char *file)
{
    FILE *fptr;
    long length;
    char *buf;

    fptr = fopen(file, "r"); /* Open file for reading */
    if (!fptr) /* Return NULL on failure */
        return NULL;
    fseek(fptr, 0, SEEK_END); /* Seek to the end of the file */
    length = ftell(fptr); /* Find out how many bytes into the file we are */
    buf = (char*)malloc(length+1); /* Allocate a buffer for the entire length of the file and a null terminator */
    fseek(fptr, 0, SEEK_SET); /* Go back to the beginning of the file */
    fread(buf, length, 1, fptr); /* Read the contents of the file in to the buffer */
    fclose(fptr); /* Close the file */
    buf[length] = 0; /* Null terminator */

    return buf; /* Return the buffer */
}

int main()
{
 char* vs;
 char* fs;

 vs = filetobuf("testshader.vs");
 fs = filetobuf("testshader.fs");

 printf("%s\n\n\n%s", vs, fs);

 free(vs);
 free(fs);

 return 0;
}

The filetobuf function is from this example http://www.opengl.org/wiki/Tutorial2:_VAOs,_VBOs,_Vertex_and_Fragment_Shaders_%28C_/_SDL%29. It seems right to me though.

So anyway, what's up with that?

Answer 1

You need to clear out your buffer - malloc doesn't do so. Try using calloc instead or memset'ing your buffer so that it starts out clear.

Answer 2

Use fopen(.... , "rb") instead of (..., "r"); Opens the file in "binary" mode under Windows.