解讀linux對string.h函數的實現

最後更新：2018-12-04 來源：互聯網

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/*
file:string.h
#ifndef _LINUX_STRING_H_
#define _LINUX_STRING_H_

/* We don't want strings.h stuff being user by user stuff by accident */

#ifdef __KERNEL__

#include <linux/types.h> /* for size_t */
#include <linux/stddef.h> /* for NULL */
#include <linux/compiler.h> /* for inline ((always_inline)) */

#ifdef __cplusplus
extern "C" {
#endif

extern char * ___strtok;
extern char * strpbrk(const char *,const char *);
extern char * strtok(char *,const char *);
extern char * strsep(char **,const char *);
extern __kernel_size_t strspn(const char *,const char *);

/*
* Include machine specific inline routines
*/
#include <asm/string.h>

#ifndef __HAVE_ARCH_STRCPY
extern char * strcpy(char *,const char *);
#endif
#ifndef __HAVE_ARCH_STRNCPY
extern char * strncpy(char *,const char *, __kernel_size_t);
#endif
#ifndef __HAVE_ARCH_STRCAT
extern char * strcat(char *, const char *);
#endif
#ifndef __HAVE_ARCH_STRNCAT
extern char * strncat(char *, const char *, __kernel_size_t);
#endif
#ifndef __HAVE_ARCH_STRCMP
extern int strcmp(const char *,const char *);
#endif
#ifndef __HAVE_ARCH_STRNCMP
extern int strncmp(const char *,const char *,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_STRNICMP
extern int strnicmp(const char *, const char *, __kernel_size_t);
#endif
#ifndef __HAVE_ARCH_STRCHR
extern char * strchr(const char *,int);
#endif
#ifndef __HAVE_ARCH_STRRCHR
extern char * strrchr(const char *,int);
#endif
#ifndef __HAVE_ARCH_STRSTR
extern char * strstr(const char *,const char *);
#endif
#ifndef __HAVE_ARCH_STRLEN
extern __kernel_size_t strlen(const char *);
#endif
#ifndef __HAVE_ARCH_STRNLEN
extern __kernel_size_t strnlen(const char *,__kernel_size_t);
#endif

#ifndef __HAVE_ARCH_MEMSET
extern void * memset(void *,int,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMCPY
extern void * memcpy(void *,const void *,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMMOVE
extern void * memmove(void *,const void *,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMSCAN
extern void * memscan(void *,int,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMCMP
extern int memcmp(const void *,const void *,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMCHR
extern void * memchr(const void *,int,__kernel_size_t);
#endif

#ifdef __cplusplus
}
#endif

#endif
#endif /* _LINUX_STRING_H_ */
*/
/*
file:string.h
#ifndef _LINUX_STRING_H_
#define _LINUX_STRING_H_

/* We don't want strings.h stuff being user by user stuff by accident */

#ifdef __KERNEL__

#include <linux/types.h> /* for size_t */
#include <linux/stddef.h> /* for NULL */
#include <linux/compiler.h> /* for inline ((always_inline)) */

#ifdef __cplusplus
extern "C" {
#endif

/*
* Include machine specific inline routines
*/
#include <asm/string.h>

#ifndef __HAVE_ARCH_MEMSET
extern void * memset(void *,int,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMCPY
extern void * memcpy(void *,const void *,__kernel_size_t);

#endif
#ifndef __HAVE_ARCH_MEMMOVE
extern void * memmove(void *,const void *,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMSCAN
extern void * memscan(void *,int,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMCMP
extern int memcmp(const void *,const void *,__kernel_size_t);
#endif
#ifndef __HAVE_ARCH_MEMCHR
extern void * memchr(const void *,int,__kernel_size_t);
#endif

#ifdef __cplusplus
}
#endif

#endif
#endif /* _LINUX_STRING_H_ */
*/

實現檔案string.c

C代碼
/*
* linux/lib/string.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
*/

/*
* stupid library routines.. The optimized versions should generally be found
* as inline code in <asm-xx/string.h>
*
* These are buggy as well..
*
* * Fri Jun 25 1999, Ingo Oeser <ioe@informatik.tu-chemnitz.de>
* - Added strsep() which will replace strtok() soon (because strsep() is
* reentrant and should be faster). Use only strsep() in new code, please.
*/

#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>

#ifndef __HAVE_ARCH_STRNICMP
/**
* strnicmp - Case insensitive(忽視大小寫), length-limited string comparison
* @s1: One string
* @s2: The other string
* @len: the maximum number of characters to compare
*/
int strnicmp(const char *s1, const char *s2, size_t len)
{
/* Yes, Virginia, it had better be unsigned */
unsigned char c1, c2;

c1 = 0; c2 = 0;
if (len) {
do {
c1 = *s1; c2 = *s2;
s1++; s2++;
//是否已到字串的末尾或兩字串是否有空串,如果到了末尾或有空串,則比較完畢
if (!c1)
break;
if (!c2)
break;
//如果沒有,且字串相等,則繼續比較下個字元
if (c1 == c2)
continue;
//如果不相同,則同時轉換為小寫字元再進行比較
c1 = tolower(c1);
c2 = tolower(c2);
//如果不相同,則比較完畢,否則繼續
if (c1 != c2)
break;
} while (--len);
}
return (int)c1 - (int)c2;
}
#endif

char * ___strtok;

#ifndef __HAVE_ARCH_STRCPY
/**
* strcpy - Copy a %NUL terminated string
* @dest: Where to copy the string to
* @src: Where to copy the string from
*/
char * strcpy(char * dest,const char *src)
{
char *tmp = dest;

while ((*dest++ = *src++) != '/0')
/* nothing */;
return tmp;
}
#endif

#ifndef __HAVE_ARCH_STRNCPY
/**
* strncpy - Copy a length-limited, %NUL-terminated string
* @dest: Where to copy the string to
* @src: Where to copy the string from
* @count: The maximum number of bytes to copy
*
* Note that unlike userspace strncpy, this does not %NUL-pad the buffer.
* However, the result is not %NUL-terminated if the source exceeds
* @count bytes.
*/
char * strncpy(char * dest,const char *src,size_t count)
{
char *tmp = dest;

while (count-- && (*dest++ = *src++) != '/0')
/* nothing */;

return tmp;
}
#endif

#ifndef __HAVE_ARCH_STRCAT
/**
* strcat - Append one %NUL-terminated string to another
* @dest: The string to be appended to
* @src: The string to append to it
*/
char * strcat(char * dest, const char * src)
{
char *tmp = dest;

while (*dest)
dest++;
while ((*dest++ = *src++) != '/0')
;

return tmp;
}
#endif

#ifndef __HAVE_ARCH_STRNCAT
/**
* strncat - Append a length-limited, %NUL-terminated string to another
* @dest: The string to be appended to
* @src: The string to append to it
* @count: The maximum numbers of bytes to copy
*
* Note that in contrast to strncpy, strncat ensures the result is
* terminated.
*/
char * strncat(char *dest, const char *src, size_t count)
{
char *tmp = dest;

if (count) { //如果追加的字元數不為0
while (*dest) //達到字串的末尾
dest++;
while ((*dest++ = *src++)) { //如果沒有到源字串末尾
if (--count == 0) { //如果已經追加了count字元
*dest = '/0';//末尾置null字元
break;//結束迴圈
}
}
}

return tmp;
}
#endif

#ifndef __HAVE_ARCH_STRCMP
/**
* strcmp - Compare two strings
* @cs: One string
* @ct: Another string
*/
int strcmp(const char * cs,const char * ct)
{
register signed char __res;

while (1) {
if ((__res = *cs - *ct++) != 0 || !*cs++)
break;
}

return __res;
}
#endif

#ifndef __HAVE_ARCH_STRNCMP
/**
* strncmp - Compare two length-limited strings
* @cs: One string
* @ct: Another string
* @count: The maximum number of bytes to compare

*/
int strncmp(const char * cs,const char * ct,size_t count)
{
register signed char __res = 0;

while (count) {
if ((__res = *cs - *ct++) != 0 || !*cs++)
break;
count--;
}

return __res;
}
#endif

#ifndef __HAVE_ARCH_STRCHR
/**
* strchr - Find the first occurrence of a character in a string
* @s: The string to be searched
* @c: The character to search for
*/
char * strchr(const char * s, int c)
{
for(; *s != (char) c; ++s)
if (*s == '/0')
return NULL;
return (char *) s;
}
#endif

#ifndef __HAVE_ARCH_STRRCHR
/**
* strrchr - Find the last occurrence of a character in a string
* @s: The string to be searched
* @c: The character to search for
*/
char * strrchr(const char * s, int c)
{
const char *p = s + strlen(s);
do {
if (*p == (char)c)
return (char *)p;
} while (--p >= s);
return NULL;
}
#endif

#ifndef __HAVE_ARCH_STRLEN
/**
* strlen - Find the length of a string
* @s: The string to be sized
*/
size_t strlen(const char * s)
{
const char *sc;

for (sc = s; *sc != '/0'; ++sc)
/* nothing */;
return sc - s;
}
#endif

#ifndef __HAVE_ARCH_STRNLEN
/**
* strnlen - Find the length of a length-limited string
* @s: The string to be sized
* @count: The maximum number of bytes to search
*/
size_t strnlen(const char * s, size_t count)
{
const char *sc;

for (sc = s; count-- && *sc != '/0'; ++sc)
/* nothing */;
return sc - s;
}
#endif

#ifndef __HAVE_ARCH_STRSPN
/**
* strspn - Calculate the length of the initial substring of @s which only
* contain letters in @accept
* @s: The string to be searched
* @accept: The string to search for
*/
size_t strspn(const char *s, const char *accept)
{
const char *p;
const char *a;
size_t count = 0;

for (p = s; *p != '/0'; ++p) {
for (a = accept; *a != '/0'; ++a) {
if (*p == *a)
break;
}
if (*a == '/0')
return count;
++count;
}

return count;
}
#endif

#ifndef __HAVE_ARCH_STRPBRK
/**
* strpbrk - Find the first occurrence of a set of characters
* @cs: The string to be searched
* @ct: The characters to search for
*/
char * strpbrk(const char * cs,const char * ct)
{
const char *sc1,*sc2;

for( sc1 = cs; *sc1 != '/0'; ++sc1) {
for( sc2 = ct; *sc2 != '/0'; ++sc2) {
if (*sc1 == *sc2)
return (char *) sc1;
}
}
return NULL;
}
#endif

#ifndef __HAVE_ARCH_STRTOK
/**
* strtok - Split a string into tokens
* @s: The string to be searched
* @ct: The characters to search for
*
* WARNING: strtok is deprecated, use strsep instead.
*/
char * strtok(char * s,const char * ct)
{
char *sbegin, *send;

sbegin = s ? s : ___strtok;
if (!sbegin) {
return NULL;
}
sbegin += strspn(sbegin,ct);
if (*sbegin == '/0') {
___strtok = NULL;
return( NULL );
}
send = strpbrk( sbegin, ct);
if (send && *send != '/0')
*send++ = '/0';
___strtok = send;
return (sbegin);
}
#endif

#ifndef __HAVE_ARCH_STRSEP
/**
* strsep - Split a string into tokens
* @s: The string to be searched
* @ct: The characters to search for
*
* strsep() updates @s to point after the token, ready for the next call.
*
* It returns empty tokens, too, behaving exactly like the libc function
* of that name. In fact, it was stolen from glibc2 and de-fancy-fied.
* Same semantics, slimmer shape.
*/
char * strsep(char **s, const char *ct)
{
char *sbegin = *s, *end;

if (sbegin == NULL)
return NULL;

end = strpbrk(sbegin, ct);
if (end)
*end++ = '/0';
*s = end;

return sbegin;
}
#endif

#ifndef __HAVE_ARCH_MEMSET
/**
* memset - Fill a region of memory with the given value
* @s: Pointer to the start of the area.
* @c: The byte to fill the area with
* @count: The size of the area.
*
* Do not use memset() to access IO space, use memset_io() instead.
*/
void * memset(void * s,int c,size_t count)
{
char *xs = (char *) s;

while (count--)
*xs++ = c;

return s;
}
#endif

#ifndef __HAVE_ARCH_BCOPY
/**
* bcopy - Copy one area of memory to another
* @src: Where to copy from
* @dest: Where to copy to
* @count: The size of the area.
*
* Note that this is the same as memcpy(), with the arguments reversed.

* memcpy() is the standard, bcopy() is a legacy BSD function.
*
* You should not use this function to access IO space, use memcpy_toio()
* or memcpy_fromio() instead.
*/
void bcopy(const void * srcp, void * destp, size_t count)
{
const char *src = srcp;
char *dest = destp;

while (count--)
*dest++ = *src++;
}
#endif

#ifndef __HAVE_ARCH_MEMCPY
/**
* memcpy - Copy one area of memory to another
* @dest: Where to copy to
* @src: Where to copy from
* @count: The size of the area.
*
* You should not use this function to access IO space, use memcpy_toio()
* or memcpy_fromio() instead.
*/
void * memcpy(void * dest,const void *src,size_t count)
{
char *tmp = (char *) dest, *s = (char *) src;

while (count--)
*tmp++ = *s++;

return dest;
}
#endif

#ifndef __HAVE_ARCH_MEMMOVE
/**
* memmove - Copy one area of memory to another
* @dest: Where to copy to
* @src: Where to copy from
* @count: The size of the area.
*
* Unlike memcpy(), memmove() copes with overlapping areas.
*/
void * memmove(void * dest,const void *src,size_t count)
{
char *tmp, *s;

if (dest <= src) {
tmp = (char *) dest;
s = (char *) src;
while (count--)
*tmp++ = *s++;
}
else {
tmp = (char *) dest + count;
s = (char *) src + count;
while (count--)
*--tmp = *--s;
}

return dest;
}
#endif

#ifndef __HAVE_ARCH_MEMCMP
/**
* memcmp - Compare two areas of memory
* @cs: One area of memory
* @ct: Another area of memory
* @count: The size of the area.
*/
int memcmp(const void * cs,const void * ct,size_t count)
{
const unsigned char *su1, *su2;
int res = 0;

for( su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)
if ((res = *su1 - *su2) != 0)
break;
return res;
}
#endif

#ifndef __HAVE_ARCH_MEMSCAN
/**
* memscan - Find a character in an area of memory.
* @addr: The memory area
* @c: The byte to search for
* @size: The size of the area.
*
* returns the address of the first occurrence of @c, or 1 byte past
* the area if @c is not found
*/
void * memscan(void * addr, int c, size_t size)
{
unsigned char * p = (unsigned char *) addr;

while (size) {
if (*p == c)
return (void *) p;
p++;
size--;
}
return (void *) p;
}
#endif

#ifndef __HAVE_ARCH_STRSTR
/**
* strstr - Find the first substring in a %NUL terminated string
* @s1: The string to be searched
* @s2: The string to search for
*/
char * strstr(const char * s1,const char * s2)
{
int l1, l2;

l2 = strlen(s2);
if (!l2)
return (char *) s1;
l1 = strlen(s1);
while (l1 >= l2) {
l1--;
if (!memcmp(s1,s2,l2))
return (char *) s1;
s1++;
}
return NULL;
}
#endif

#ifndef __HAVE_ARCH_MEMCHR
/**
* memchr - Find a character in an area of memory.
* @s: The memory area
* @c: The byte to search for
* @n: The size of the area.
*
* returns the address of the first occurrence of @c, or %NULL
* if @c is not found
*/
void *memchr(const void *s, int c, size_t n)
{
const unsigned char *p = s;
while (n-- != 0) {
if ((unsigned char)c == *p++) {
return (void *)(p-1);
}
}
return NULL;
}

#endif

本文章原先以中文撰寫並發佈於 aliyun.com，亦設英文版本，僅作資訊用途。本網站不對文章的準確性，完整性或可靠性或其任何翻譯作出任何明示或暗示的陳述或保證。如對該文章有任何疑慮或投訴，請傳送電郵至 info-contact@alibabacloud.com 並提供相關疑慮或投訴的詳細說明。職員會於 5 個工作天內與您聯絡，一經驗證之後，即會刪除該侵權內容。

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