fread(S)                       6 January 1993                       fread(S)


 Name

    fread, fwrite - binary input/output

 Syntax


    cc  . . .  -lc


    #include  <stdio.h>
    #include  <sys/types.h>

    size_t fread (ptr, size, nitems, stream)
    void *ptr;
    size_t size;
    int nitems;
    FILE *stream;

    size_t fwrite (ptr, size, nitems, stream)
    void *ptr;
    size_t size;
    int nitems;
    FILE *stream;


    SVID Syntax


    int fread (ptr, size, nitems, stream)
    void *ptr;
    size_tsize;
    int nitems;
    FILE *stream;

    int fwrite (ptr, size, nitems, stream)
    void *ptr;
    size_t size;
    int nitems;
    FILE *stream;


 Description

    The fread function copies nitems items of data from the named input
    stream into an array pointed to by ptr.  An item of data is a sequence of
    bytes (not necessarily terminated by a null byte) of length size.  fread
    stops appending bytes if an end-of-file or error condition is encountered
    while reading stream, or if nitems items have been read.  fread leaves
    the file pointer in stream, if defined, pointing to the byte following
    the last byte read if there is a byte.  fread does not change the con-
    tents of stream.

    fwrite appends at most nitems items of data from the array pointed to by
    ptr to the named output stream.  fwrite stops appending when it has
    appended nitems items of data or if an error condition is encountered on
    stream.  fwrite does not change the contents of the array pointed to by
    ptr.

    The argument size is typically sizeof(*ptr) where the pseudo-function
    sizeof specifies the length of an item pointed to by ptr.  If ptr points
    to a data type other than char, it should be cast into a pointer to char.

 Diagnostics

    The fread and fwrite functions return the number of items read or writ-
    ten.  If nitems is non-positive, no characters are read or written, and 0
    is returned by both fread and fwrite.

 See also

    fopen(S), getc(S), gets(S), printf(S), putc(S), puts(S), read(S),
    scanf(S), stdio(S) write(S)

 Standards conformance

    fread and fwrite are conformant with:
    AT&T SVID Issue 2;
    X/Open Portability Guide, Issue 3, 1989;
    ANSI X3.159-1989 Programming Language -- C;
    Intel386 Binary Compatibility Specification, Edition 2 (iBCSe2);
    IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C
    Language] (ISO/IEC 9945-1);
    and NIST FIPS 151-1.