char *strtok(char *str, const char *delim)數組
會修改數據源。外部加鎖才線程安全(strtok執行結束再解鎖執行另外一個strtok循環知道工做完成)安全
主要是以互斥訪問strtok實現文件中的static外部變量char*old。源碼以下。ide
#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)this
會修改數據源。可重入的,注意這裏雖然改動stringp的內容,主要是不在使用static靜態變量了。spa
#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; }
注意事項,會屢次出現空字符串的問題,這是由於strsep在處理多於一個的delimit字符是會返回空字\0符串代替NULL(見源碼便知),http://blog.csdn.net/striver1205/article/details/25601885.net
對比strtok,man手冊提到:線程
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.指針
stringp必須是二級指針,不能是指向字符數組的指針!code
正確用法:orm
char a[]=......;char *p=a;strsep(&p,delim)
錯誤用法:
char a[]=...;strsep(&a,delim);會包參數類型錯誤
錯誤用法:
char *a=」xxxxx」;strsep(&a,delim)//錯誤,注意原串會被修改內容,字符常量會seg fault
char *strtok_r(char *str, const char *delim, char **saveptr)
會修改數據源。可重入,理由和strsep相似。