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.
Example
#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"); } } }
Output:
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
(C11)(C11)(C11) | reads formatted input from stdin , a file stream or a buffer (function) |
gets a character string from a file stream (function) | |
writes to a file (function) | |
C++ documentation for fread |
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