fread, fwrite − binary stream input/output
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
fwrite(const void *ptr, size_t
size, size_t nmemb,
The function fread() reads nmemb items of data, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr.
The function fwrite() writes nmemb items of data, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.
For nonlocking counterparts, see unlocked_stdio(3).
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).
For an explanation of the terms used in this section, see attributes(7).
POSIX.1-2001, POSIX.1-2008, C89.
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