# fread

From cppreference.com
< c‎ | io

Defined in header `<stdio.h>` |  |
size_t fread( void *buffer, size_t size, size_t count, FILE *stream ); |  | (until C99)
size_t fread( void *restrict buffer, size_t size, size_t count, FILE *restrict stream ); |  | (since C99)

Reads up to `count` objects into the array `buffer` from the given input stream `stream` as if by calling fgetc `size` times for each object, and storing the results, in the order obtained, into the successive positions of `buffer`, which is reinterpreted as an array of unsigned char. The file position indicator for the stream is advanced by the number of characters read.

If an error occurs, the resulting value of the file position indicator for the stream is indeterminate. If a partial element is read, its value is indeterminate.

### Parameters

buffer | - | pointer to the array where the read objects are stored
size | - | size of each object in bytes
count | - | the number of the objects to be read
stream | - | the stream to read

### Return value

Number of objects read successfully, which may be less than `count` if an error or end-of-file condition occurs.

If `size` or `count` is zero, `fread` returns zero and performs no other action.

`fread` does not distinguish between end-of-file and error, and callers must use feof and ferror to determine which occurred.

### Example

Run this code

    #include <stdio.h>

    enum { SIZE = 5 };
    int main(void)
    {
        double a[SIZE] = {1.,2.,3.,4.,5.};
        FILE *fp = fopen("test.bin", "wb"); // must use binary mode
        fwrite(a, sizeof *a, SIZE, fp); // writes an array of doubles
        fclose(fp);

        double b[SIZE];
        fp = fopen("test.bin","rb");
        size_t ret_code = fread(b, sizeof *b, SIZE, fp); // reads an array of doubles
        if(ret_code == SIZE) {
            puts("Array read successfully, contents: ");
            for(int n = 0; n < SIZE; ++n) printf("%f ", b[n]);
            putchar('\n');
        } else { // error handling
           if (feof(fp))
              printf("Error reading test.bin: unexpected end of file\n");
           else if (ferror(fp)) {
               perror("Error reading test.bin");
           }
        }

        fclose(fp);
    }

Output:

    Array read successfully, contents:
    1.000000 2.000000 3.000000 4.000000 5.000000

### References

- C11 standard (ISO/IEC 9899:2011):

  - 7.21.8.1 The fread function (p: 335)

- C99 standard (ISO/IEC 9899:1999):

  - 7.19.8.1 The fread function (p: 301)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.9.8.1 The fread function

### See also

scanf fscanf sscanf scanf_s fscanf_s sscanf_s (C11)(C11)(C11) | reads formatted input from stdin, a file stream or a buffer (function)
fgets | gets a character string from a file stream (function)
fwrite | writes to a file (function)
C++ documentation for fread

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=c/io/fread&oldid=91113"