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fread() does not reach EOF in C

Hi, this is a beginner question.

Code:

#include <stdint.h>

#include <stdio.h>

#include <stdlib.h>



// Define block size

#define BLOCK 512



void function(char *argv);



int main(int argc, char *argv[])

{

    // Accept one input file

    if (argc != 2)

    {

        printf("Usage: ./Test inputfile\n");

        return 1;

    }



    // printf("argv: %s", argv[1]);



    // Open file and check success, as otherwise defaults to NULL.

    FILE *file = fopen(argv[1], "r");



    if (file == NULL)

    {

        printf("File not valid.\n");

        return 1;

    }



    // Allocate memory buffer with the defined block size

    uint8_t *buffer = malloc(BLOCK * sizeof(uint8_t));

    int counter = 0;



    

    while (fread(buffer, BLOCK, 1, file) != EOF)

    {

        // Printf as a test until EOF 

        printf("test\n");



        // Do something...

    }

    

    // Free memory and close file

    free(buffer);

    fclose(file);





    return 0;

}

This programme should read an input file in 512 byte blocks until reaching EOF, which it does not seem to reach. The line for `printf("test\n") I added prints lines of test indefinitely. Can anyone tell me what I am doing wrong?

Thanks.

Your code assumes that fread returns the value of the byte read, which could be EOF. It doesn't. It returns the number of "blocks" read.

So it should be:

Code:

while (fread(buffer, BLOCK, 1, file)) {

or for more readable

Code:

while (fread(buffer, BLOCK, 1, file) > 0) 

  {

  // do something

  }

Quote:

Originally Posted by lxs602 (Post 6483886)

[snip]

This programme should read an input file in 512 byte blocks until reaching EOF, which it does not seem to reach. The line for `printf("test\n") I added prints lines of test indefinitely. Can anyone tell me what I am doing wrong?

Thanks.

From the fread(3) manpage:

Code:

RETURN VALUE

      On  success,  fread()  and  fwrite()  return the number of items read or written.  This number

      equals the number of bytes transferred only when size is 1.  If an error occurs, or the end of

      the file is reached, the return value is a short item count (or zero).



      fread() does not distinguish between end-of-file and error, and callers must use feof(3) and

      ferror(3) to determine which occurred.

One thing to try: Looping on calls to feof and freading only if it returns "nope, not at EOF yet.

Hope this points to a solution...

Reply #2 uses the fact that "zero is 'false-y'" and thus ends the while loop. This is very commonly done. But, the equivalent reply #3 is more explicit.

Another solution is to find out the size of the file and read the entire file in 1 shot.

Code:

int fileSize;

FILE *file = fopen(argv[1], "r");

fseek(file, 0, SEEK_END);                //Go to end of file

fileSize=(int)ftell(file);        //This returns a long, which is 32 bit (64 bit warning!)

fclose(file);



file = fopen(argv[1], "r");

if(fread(buffer, 1, fileSize, file)< fileSize)

{

Error Detected;

}



fclose(file);