ref: 276c090a9536c0165d10d908862a93e743d3b344
dir: /sys/man/2/memory/
.TH MEMORY 2 .SH NAME memccpy, memchr, memcmp, memcpy, memmove, memset, tsmemcmp \- memory operations .SH SYNOPSIS .B #include <u.h> .br .B #include <libc.h> .PP .ta \w'\fLvoid* 'u .B void* memccpy(void *s1, void *s2, int c, usize n) .PP .B void* memchr(void *s, int c, usize n) .PP .B int memcmp(void *s1, void *s2, usize n) .PP .B void* memcpy(void *s1, void *s2, usize n) .PP .B void* memmove(void *s1, void *s2, usize n) .PP .B void* memset(void *s, int c, usize n) .PP .B #include <libsec.h> .PP .B int tsmemcmp(void *s1, void *s2, ulong n) .SH DESCRIPTION These functions operate efficiently on memory areas (arrays of bytes bounded by a count, not terminated by a zero byte). They do not check for the overflow of any receiving memory area. .PP .I Memccpy copies bytes from memory area .I s2 into .IR s1 , stopping after the first occurrence of byte .I c has been copied, or after .I n bytes have been copied, whichever comes first. It returns a pointer to the byte after the copy of .I c in .IR s1 , or zero if .I c was not found in the first .I n bytes of .IR s2 . .PP .I Memchr returns a pointer to the first occurrence of byte .I c in the first .I n bytes of memory area .IR s, or zero if .I c does not occur. .PP .I Memcmp compares its arguments, looking at the first .I n bytes only, and returns an integer less than, equal to, or greater than 0, according as .I s1 is lexicographically less than, equal to, or greater than .IR s2 . The comparison is bytewise unsigned. .PP .I Memcpy copies .I n bytes from memory area .I s2 to .IR s1 . It returns .IR s1 . .PP .I Memmove works like .IR memcpy , except that it is guaranteed to work if .I s1 and .IR s2 overlap. .PP .I Memset sets the first .I n bytes in memory area .I s to the value of byte .IR c . It returns .IR s . .PP .I Tsmemcmp is a variant of .I memcmp that is safe against timing attacks. It does not stop when it sees a difference, this way it's runtime is function of .I n and not something that can lead clues to attackers. .SH SOURCE All these routines have portable C implementations in .BR /sys/src/libc/port . Most also have machine-dependent assembly language implementations in .BR /sys/src/libc/$objtype . .I Tsmemcmp is found on .BR /sys/src/libsec/port/tsmemcmp.c . .SH SEE ALSO .IR strcat (2) .SH BUGS ANSI C does not require .I memcpy to handle overlapping source and destination; on Plan 9, it does, so .I memmove and .I memcpy behave identically. .PP If .I memcpy and .I memmove are handed a negative count, they abort. .PP .I Memcmp should not be used to compare sensitive data as it's vulnerable to timing attacks. Instead, .I tsmemcmp should be used.