关于字符串操作的一些函数简单说明与应用
1 strcasecmp, strncasecmp
此函数类似与 strcmp，比较字串符，只是对大小写不敏感（不区分）
int main (void )
{
int retval = -1;
const char *psrc = "Hello,World!";
// const char *pdst = "hello,World!";
const char *pdst = "Hello,World!";
size_t sSrcLen = strlen( psrc );
/* NAME
strcmp, strncmp - compare two strings
* SYNOPSIS
#include <string.h>
int strcmp(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t n);
* DESCRIPTION
The strcmp() function compares the two strings s1 and s2.
It returns an integer less than, equal to, or greater than zero if s1 is found,
respectively, to be less than, to match, or be greater than s2.
The strncmp() function is similar, except it only compares the first (at most) n characters of s1 and s2.
* RETURN VALUE
The strcmp() and strncmp() functions return an integer less than, equal to,
or greater than zero if s1 (or the first n bytes thereof) is found, respectively,
to be less than, to match, or be greater than s2.
*/
retval = strcmp( psrc, pdst);
printf("[%s]-[%d]: retval = %d \n", __func__, __LINE__, retval);
retval = strncmp( psrc, pdst, sSrcLen);
printf("[%s]-[%d]: retval = %d \n", __func__, __LINE__, retval);
/* NAME
strcasecmp, strncasecmp - compare two strings ignoring case
* SYNOPSIS
#include <strings.h>
int strcasecmp(const char *s1, const char *s2);
int strncasecmp(const char *s1, const char *s2, size_t n);
* DESCRIPTION
The strcasecmp() function compares the two strings s1 and s2,
ignoring the case of the characters. // 忽略字母的大小写， (重点，与上面函数的区别)
It returns an integer less than, equal to, or greater than zero
if s1 is found, respectively, to be less than, to match, or be greater than s2.
The strncasecmp() function is similar, except it only compares the first n characters of s1.
*RETURN VALUE
The strcasecmp() and strncasecmp() functions return an integer less than,
equal to, or greater than zero if s1 (or the first n bytes thereof) is found,
respectively,to be less than, to match, or be greater than s2.
*/
retval = strcasecmp( psrc, pdst);
printf("[%s]-[%d]: retval = %d \n", __func__, __LINE__, retval);
retval = strncasecmp( psrc, pdst, sSrcLen);
printf("[%s]-[%d]: retval = %d \n", __func__, __LINE__, retval);
return 0;
}
2 strstr, strcasestr
在源字串中寻找子字符串，一个对大小写敏感，前面函数对大小写不敏感
int main (void )
{
const char *pSrc = "HelloworldComeon!";
// const char *pDst = "heLLo";
// const char *pDst = "WoRld";
const char *pDst = "come";
/* NAME
strstr, strcasestr - locate a substring
* SYNOPSIS
#include <string.h>
char *strstr(const char *haystack, const char *needle);
#define _GNU_SOURCE
#include <string.h>
char *strcasestr(const char *haystack, const char *needle);
* DESCRIPTION
The strstr() function finds the first occurrence of the substring needle in the string haystack.
The terminating '\0' characters are not compared.
The strcasestr() function is like strstr(), but ignores the case of both arguments.
* RETURN VALUE
These functions return a pointer to the beginning of the substring, or NULL if the substring is not found.
*/
char *pRetval = strstr( (char *)pSrc, pDst);
printf("[%s]-[%d] pRetval = %s \n", __func__, __LINE__, pRetval);
/* 个人理解： 在源字符串中需找目标字符串，如果源字符串中存在，则返回出现目标字符串的首地址，不存在，则返回空
对大小写字母敏感(区分大小写)*/
pRetval = strcasestr( (char *)pSrc, pDst );
printf("[%s]-[%d] pRetval = %s \n", __func__, __LINE__, pRetval);
/* 个人理解： 在源字符串中需找目标字符串，如果源字符串中存在，则返回出现目标字符串的首地址，不存在，则返回空
对大小写字母不敏感(忽略大小写)*/
return 0;
}
3 strchr strrchr,
在字符串中查找对应ASCII码为对应正数的字节，前面函数返回第一次查找到，后面函数返回最后一次查找到
int main (void )
{
/* NAME
strchr, strrchr, -locate character in string
SYNOPSIS
#include <string.h>
char *strchr(const char *s, int c);
char *strrchr(const char *s, int c);
DESCRIPTION
The strchr() function returns a pointer to the first occurrence of the character c in the string s.
The strrchr() function returns a pointer to the last occurrence of the character c in the string s.
RETURN VALUE
The strchr() and strrchr() functions return a pointer to the matched character or NULL if the character is not found.
*/
const char *pSrc = "xxxxbooooobwwwwwwwbppppppbcccccccc";
char *pRetval = strchr((char*)pSrc, 98);
printf("[%s]-[%d] pRetval = %s \n", __func__, __LINE__, pRetval);
/* 个人理解：在目标字符串中，从字符串开头开始查找对已ASCII码为98的字节，
如果存在，则返回第一次查找到的字节地址，
不存在，则返回空*/
pRetval = strrchr((char*)pSrc, 98);
printf("[%s]-[%d] pRetval = %s \n", __func__, __LINE__, pRetval);
/* 个人理解：在目标字符串中，从字符串开头开始查找对已ASCII码为98的字节，
如果存在，则返回最后一次查找到的字节地址，
不存在，则返回空*/
return 0; } ~4 strcoll 比较字符串
int main (void )
{
/*
* like the strcmp
*/
return 0;
}
~
~
5 strdup
类似与字符串拷贝函数，只是需要手动释放返回的字符串地址
int main (void )
{
/* NAME
strdup, strndup - duplicate a string
* SYNOPSIS
#include <string.h>
char *strdup(const char *s);
char *strndup(const char *s, size_t n);
* DESCRIPTION
The strdup() function returns a pointer to a new string which is a duplicate of the string s.
Memory for the new string is obtained with malloc(3), and can be freed with free(3).
The strndup() function is similar, but only copies at most n characters.
If s is longer than n, only n characters are copied, and a terminating null byte ('\0') is added.
* RETURN VALUE
The strdup() function returns a pointer to the duplicated string, or NULL if insufficient memory was available.
*/
const char *pSrc = "Hello, world!";
char *pRetval = strdup( pSrc );
printf("[%s]-[%d] pRetval = %s \n", __func__, __LINE__, pRetval);
/* 复制目标字符串，返回字符串的内存地址需要自己手动释放 */
if( pRetval != NULL )
{
free( pRetval );
pRetval = NULL;
}
pRetval = strndup( pSrc, 4);
/* 复制指定长度目标字符串，返回字符串的内存地址需要自己手动释放 */
printf("[%s]-[%d] pRetval = %s \n", __func__, __LINE__, pRetval);
if( pRetval != NULL )
{
free( pRetval );
pRetval = NULL;
}
return 0;
}
6 strsep
分解字符串
int main (void )
{
/* NAME
strsep - extract token from string
* SYNOPSIS
#include <string.h>
char *strsep(char **stringp, const char *delim);
* DESCRIPTION
If *stringp is NULL, the strsep() function returns NULL and does nothing else.
Otherwise, this function finds the first token in the string *stringp, where tokens
are delimited by symbols in the string delim. This token is terminated with a '\0' character (by overwriting the delimiter)
and *stringp is updated to point past the token. In case no delimiter was found,
the token is taken to be the entire string *stringp, and *stringp is made NULL.
* RETURN VALUE
The strsep() function returns a pointer to the token, that is, it returns the original value of *stringp.
* BUGS
Be cautious when using this function. If you do use it, note that:
* This function modifies its first argument.
* This function cannot be used on constant strings.
* The identity of the delimiting character is lost.
*/
char pSrc[] ="www.baidu.com.cn.education.mahuateng";
char *pStringgp = pSrc;
char *pRetval = NULL;
while( (pRetval = strsep(&pStringgp, ".")) != NULL )
/* 个人理解：分解字符串为一组字符串, 此函数会改变字符串， 返回开始到 第一个出现 delim 的地方
并用 ‘\0’替换出现的第一个delim子字符串，如果没有 delim，则返回NULL,
此函数 比strtok好处是接受空字符串并且是线程安全的。
切割后源字符串变为第一个delim 到stringp 末尾,并过滤掉第一个delim。
如果stringp 为NULL,则返回NULL, */
{
printf("[%s]-[%d] pStringgp = %s \n", __func__, __LINE__, pStringgp);
printf("[%s]-[%d] pRetval = %s \n", __func__, __LINE__, pRetval);
}
/* 总结：strsep返回值为分割后的开始字符串，
并将函数的第一个参数指针指向分割后的剩余字符串。
它适用于分割关键字在两个字符串之间只严格出现一次的情况 */
return 0; }
7 strtok
通过分隔子字符串，分割目标字符串
int main (void )
{
/* NAMEstrtok - extract tokens from strings
* SYNOPSIS
#include <string.h>
char *strtok(char *str, const char *delim);
* DESCRIPTION
The strtok() function parses a string into a sequence of tokens.
On the first call to strtok() the string to be parsed should be specified in str.
In each subsequent call that should parse the same string, str should be NULL.
The delim argument specifies a set of characters that delimit the tokens in the parsed string.
The caller may specify different strings in delim in successive calls that parse the same string.
Each call to strtok() returns a pointer to a null-terminated string containing the next token.
This string does not include the delimiting character. If no more tokens are found, strtok() returns NULL.
A sequence of two or more contiguous delimiter characters in the parsed string is considered to be a single delimiter.
Delimiter characters at the start or end of the string are ignored. Put another way: the tokens returned by strtok() are always non-empty strings.
* RETURN VALUE
The strtok() functions return a pointer to the next token, or NULL if there are no more tokens.
*/
char pSrc[] = "www.baidu.com.education.mahuateng";
char *pRetval = NULL;
printf("[%s]-[%d] pSrc = %s\n", __func__, __LINE__, pSrc);
pRetval = strtok( (char *)pSrc, ".");
/* 个人理解：以"."子字符串为分隔符，分解目标字符串为一组子字符串，并且过滤掉分隔符如果有子串分隔符的话，则将此处分隔符更改为'\0'，目标字符串因此也发生改变，
当再次在以前的字符串中分解字串的话，则需要要把目标字串的参数置NULL，
不存在则返回NULL*/
while( NULL != pRetval )
{
printf("[%s]-[%d] pRetval = %s\n", __func__, __LINE__, pRetval);
pRetval = strtok( NULL, ".");
}
printf("[%s]-[%d] pSrc = %s\n", __func__, __LINE__, pSrc);
/* 总结：strtok内部记录上次调用字符串的位置，
所以不支持多线程，可重入版本为strtok_r,有兴趣的可以研究一下。
它适用于分割关键字在字符串之间是“单独”或是 “连续“在一起的情况。 */
return 0; }