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MEMSET(3)             DragonFly Library Functions Manual             MEMSET(3)


NAME

     memset, memset_s - write a byte to byte string


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <string.h>

     void *
     memset(void *dest, int c, size_t len);

     errno_t
     memset_s(void *dest, rsize_t destsz, int c, rsize_t len);


DESCRIPTION

     The memset() function writes len bytes of value c (converted to an
     unsigned char) to the string dest.  Undefined behaviour from memset(),
     resulting from storage overflow, will occur if len is greater than the
     the length of buffer dest.  The behaviour is also undefined if dest is an
     invalid pointer.

     The memset_s() function behaves the same as memset() except that an error
     is returned and the currently registered runtime-constraint handler is
     called if dest is a null pointer, destsz or len is greater than
     RSIZE_MAX, or len is greater than destsz (buffer overflow would occur).
     The runtime-constraint handler is called first and may not return.  If it
     does return, an error is returned to the caller.  Like explicit_bzero(3),
     memset_s() is not removed through Dead Store Elimination (DSE), making it
     useful for clearing sensitive data.  In contrast memset() function may be
     optimized away if the object modified by the function is not accessed
     again.  To clear memory that will not subsequently be accessed it is
     advised to use memset_s() instead of memset().  For instance, a buffer
     containing a password should be cleared with memset_s() before free(3).


RETURN VALUES

     The memset() function returns its first argument.  The memset_s()
     function returns zero on success, non-zero on error.


SEE ALSO

     bzero(3), explicit_bzero(3), set_constraint_handler_s(3), swab(3),
     wmemset(3)


STANDARDS

     The memset() function conforms to ISO/IEC 9899:1990 ("ISO C90").
     memset_s() conforms to ISO/IEC 9899:2011 ("ISO C11") K.3.7.4.1.

DragonFly 5.7-DEVELOPMENT     September 14, 2019     DragonFly 5.7-DEVELOPMENT

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