string.3

操作系统设计与实现源码

.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)string.3	6.1 (Berkeley) 5/15/85
.\"
.TH STRING 3  "May 15, 1985"
.UC 4
.SH NAME
string, strcat, strncat, strcmp, strncmp, strcpy, strncpy, strlen, index, rindex \- string operations
string, strcat, strncat, strcmp, strncmp, strcpy, strncpy, strlen, strchr, strrchr, strerror, memcmp, memcpy, memmove, memchr, memset, index, rindex \- string operations
.SH SYNOPSIS
.nf
.ft B
#include <sys/types.h>
#include <strings.h>

char *strcat(char *\fIs1\fP, const char *\fIs2\fP)
char *strncat(char *\fIs1\fP, const char *\fIs2\fP, size_t \fIn\fP)
int strcmp(const char *\fIs1\fP, const char *\fIs2\fP)
int strncmp(const char *\fIs1\fP, const char *\fIs2\fP, size_t \fIn\fP)
char *strcpy(char *\fIs1\fP, const char *\fIs2\fP)
char *strncpy(char *\fIs1\fP, const char *\fIs2\fP, size_t \fIn\fP)
size_t strlen(const char *\fIs\fP)
char *strchr(const char *\fIs\fP, int \fIc\fP)
char *strrchr(const char *\fIs\fP, int \fIc\fP)
char *strerror(int \fIerrnum\fP)
int memcmp(const void *\fIs1\fP, const void *\fIs2\fP, size_t \fIn\fP)
void *memcpy(void *\fIs1\fP, const void *\fIs2\fP, size_t \fIn\fP)
void *memmove(void *\fIs1\fP, const void *\fIs2\fP, size_t \fIn\fP)
void *memchr(const void *\fIs\fP, int \fIc\fP, size_t \fIn\fP)
void *memset(void *\fIs\fP, int \fIc\fP, size_t \fIn\fP)
char *index(const char *\fIs\fP, int \fIc\fP)
char *rindex(const char *\fIs\fP, int \fIc\fP)
.ft R
.fi
.SH DESCRIPTION
These functions operate on null-terminated strings.
They do not check for overflow of any receiving string.
.PP
.B Strcat
appends a copy of string
.I s2
to the end of string
.IR s1 .
.B Strncat
copies at most
.I n
characters.  Both return a pointer to the null-terminated result.
.PP
.B Strcmp
compares its arguments and returns an integer
greater than, equal to, or less than 0, according as
.I s1
is lexicographically greater than, equal to, or less than
.IR s2 .
.B Strncmp
makes the same comparison but looks at at most
.I n
characters.
.PP
.B Strcpy
copies string
.I s2
to
.IR s1 ,
stopping after the null character has been moved.
.B Strncpy
copies exactly
.I n
characters, truncating or null-padding
.I s2;
the target may not be null-terminated if the length of
.I s2
is
.I n
or more.  Both return
.IR s1 .
.PP
.B Strlen
returns the number of non-null characters in
.IR s .
.PP
.B Strchr
.RB ( strrchr )
returns a pointer to the first (last) occurrence of character 
.I c
in string
.I s,
or null if
.I c
does not occur in the string.
.PP
.B Strerror
returns the error string for the system call error
.IR errnum .
See
.BR intro (2).
.PP
.B Memcmp
is like
.B strcmp
except that the strings are memory blocks of length
.IR n .
Null characters are treated as ordinary characters.
.PP
.B Memcpy
copies
.I n
bytes from the location pointed to by
.I s2
to
.IR s1 .
.B Memmove
is like memcpy, except that it can handle overlap between the two strings.
Both functions return
.IR s1 .
.PP
.B Memchr
returns a pointer to the first occurrence of character
.I c
in string
.I s,
or null if
.I c
does not occur in the string.
.PP
.B Memset
sets
.I n
bytes to
.I c
starting at location
.IR s .
It returns
.IR s .
.PP
.B Index
and
.B rindex
are obsolete versions of
.B strchr
and
.BR strrchr .
New code should avoid using them.
.SH NOTES
Characters are compared as
.BR "unsigned char" ,
whether
.B char
itself is signed or not.