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char *strtok(char *str, const char *delim)
会修改数据源。外部加锁才线程安全（strtok执行结束再解锁执行另一个strtok循环知道工作完成）
主要是以互斥访问strtok实现文件中的static外部变量char*old。源码如下。
#include <string.h> static char *olds; #undef strtok /* Parse S into tokens separated by characters in DELIM. If S is NULL, the last string strtok() was called with is used. For example: char s[] = "-abc-=-def"; x = strtok(s, "-"); // x = "abc" x = strtok(NULL, "-="); // x = "def" x = strtok(NULL, "="); // x = NULL // s = "abc\0=-def\0" */ char * strtok (s, delim) char *s; const char *delim; { char *token; if (s == NULL) s = olds; /* Scan leading delimiters. */ s += strspn (s, delim); if (*s == ‘\0‘) { olds = s; return NULL; } /* Find the end of the token. */ token = s; s = strpbrk (token, delim); if (s == NULL) /* This token finishes the string. */ olds = __rawmemchr (token, ‘\0‘); else { /* Terminate the token and make OLDS point past it. */ *s = ‘\0‘; olds = s + 1; } return token; }
char *strsep(char **stringp, const char *delim)
会修改数据源。可重入的，注意这里和stringp的改动无关，主要是不在使用static静态变量了。
#include <string.h> #undef __strsep #undef strsep char * __strsep (char **stringp, const char *delim) { char *begin, *end; begin = *stringp; if (begin == NULL) return NULL; /* A frequent case is when the delimiter string contains only one character. Here we don‘t need to call the expensive `strpbrk‘ function and instead work using `strchr‘. */ if (delim[0] == ‘\0‘ || delim[1] == ‘\0‘) { char ch = delim[0]; if (ch == ‘\0‘) end = NULL; else { if (*begin == ch) end = begin; else if (*begin == ‘\0‘) end = NULL; else end = strchr (begin + 1, ch); } } else /* Find the end of the token. */ end = strpbrk (begin, delim); if (end) { /* Terminate the token and set *STRINGP past NUL character. */ *end++ = ‘\0‘; *stringp = end; } else /* No more delimiters; this is the last token. */ *stringp = NULL; return begin; }
注意事项，会多次出现空字符串的问题，这是因为strsep在处理多于一个的delimit字符是会返回空字\0符串代替NULL（见源码便知），http://blog.csdn.net/striver1205/article/details/25601885
strsep甚至更改了原串的指针指向。。。这是其他俩函数没有的。man手册提到：
The strsep() function was introduced as a replacement for strtok(3), since the latter cannot handle empty fields.
However, strtok(3) conforms to C89/C99 and hence is more portable.
char *strtok_r(char *str, const char *delim, char **saveptr)
会修改数据源。可重入。
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原文地址：http://www.cnblogs.com/zhaoyl/p/5774134.html
