fwrite
From cppreference.com
| Defined in header <stdio.h>
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| (until C99) | ||
| (since C99) | ||
Writes count of objects from the given array buffer to the output stream stream. The objects are written as if by reinterpreting each object as an array of unsigned char and calling fputc size times for each object to write those unsigned chars into stream, in order. The file position indicator for the stream is advanced by the number of characters written.
If an error occurs, the resulting value of the file position indicator for the stream is indeterminate.
Parameters
| buffer | - | pointer to the first object in the array to be written |
| size | - | size of each object |
| count | - | the number of the objects to be written |
| stream | - | pointer to the output stream |
Return value
The number of objects written successfully, which may be less than count if an error occurs.
If size or count is zero, fwrite returns zero and performs no other action.
Example
Run this code
#include <stdio.h> #include <stdlib.h> #include <assert.h> enum { SIZE = 5 }; int main(void) { double a[SIZE] = {1, 2, 3, 4, 5}; FILE *f1 = fopen("file.bin", "wb"); assert(f1); size_t r1 = fwrite(a, sizeof a[0], SIZE, f1); printf("wrote %zu elements out of %d requested\n", r1, SIZE); fclose(f1); double b[SIZE]; FILE *f2 = fopen("file.bin", "rb"); size_t r2 = fread(b, sizeof b[0], SIZE, f2); fclose(f2); printf("read back: "); for(size_t i = 0; i < r2; i++) printf("%0.2f ", b[i]); }
Output:
wrote 5 elements out of 5 requested read back: 1.00 2.00 3.00 4.00 5.00
References
- C11 standard (ISO/IEC 9899:2011):
- 7.21.8.2 The fwrite function (p: 335-336)
- C99 standard (ISO/IEC 9899:1999):
- 7.19.8.2 The fwrite function (p: 301-302)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.9.8.2 The fwrite function
See also
| (C99)(C11)(C11)(C11)(C11) |
prints formatted output to stdout, a file stream or a buffer (function) |
| writes a character string to a file stream (function) | |
| reads from a file (function) |