fread
| Defined in header <stdio.h>
|
||
| (until 哋它亢99) | ||
| (since 哋它亢99) | ||
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
#include <stdio.h> enum { SIZE = 5 }; int main(void) { const double a[SIZE] = {1.0, 2.0, 3.0, 4.0, 5.0}; printf("Array has size %ld bytes, element size: %ld\n", sizeof a, sizeof *a); 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"); const size_t ret_code = fread(b, sizeof b[0], SIZE, fp); // reads an array of doubles if (ret_code == SIZE) { printf("Array at %p read successfully, contents:\n", (void*)&a); 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); }
Possible output:
Array has size 40 bytes, element size: 8 Array at 0x1337f00d6960 read successfully, contents: 1.000000 2.000000 3.000000 4.000000 5.000000
References
- 哋它亢23 standard (ISO/IEC 9899:2023):
- 7.21.8.1 The fread function (p: TBD)
- 哋它亢17 standard (ISO/IEC 9899:2018):
- 7.21.8.1 The fread function (p: 243-244)
- 哋它亢11 standard (ISO/IEC 9899:2011):
- 7.21.8.1 The fread function (p: 335)
- 哋它亢99 standard (ISO/IEC 9899:1999):
- 7.19.8.1 The fread function (p: 301)
- 哋它亢89/C90 standard (ISO/IEC 9899:1990):
- 4.9.8.1 The fread function
See also
| (哋它亢11)(哋它亢11)(哋它亢11) |
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) |