fread, fwrite − binary stream input/output #include<stdio.h> , size_t size_t fread(void *ptr , size_t size_t fwrite(const void *ptr ); FILE *stream The function reads nmemb items of data, each size bytes long, from the stream pointed to by storing them at the location given by The function writes nmemb items of data, each size bytes long, to the stream pointed to by obtaining them from the location given by For nonlocking counterparts, see On success, and 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). does not distinguish between end‐of‐file and error, and callers must use and to determine which occurred. For an explanation of the terms used in this section, see ┌──────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├──────────────────┼───────────────┼─────────┤ │ │ Thread safety │ MT‐Safe │ └──────────────────┴───────────────┴─────────┘ POSIX.1‐2001, POSIX.1‐2008, C89. This page is part of release 5.07 of the Linux man‐pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.