头文件regex.h中定义了c/c++使用正则表达式的函数： regcomp(), regexec(), regerror(), and regfree() 。regcomp()编译正则表达式，regexec()匹配正则表达式， regfree()释放正则表达式，regerror()报告正则表达式错误信息。使用方法如下代码所示：
static string merge_path(const string base, const string path)
{
static regex_t re;
static int initialized = 0;
regmatch_t pm[1];
string p, s;
size_t len;
assert(*path != '/');
if (base && (p = strrchr(base, '/'))) {
newarray(s, (p - base) + strlen(path) + 2);
strncpy(s, base, (p - base) + 1);
strcpy(s + ((p - base) + 1), path);
} else {
newarray(s, strlen(path) + 2);
#if 0
s[0] = '/';
strcpy(s + 1, path);
#else
strcpy(s, path);
#endif
}
/* Replace all substrings of form "/xxx/../" with "/" */
if (! initialized) {
assert(regcomp(&re, "/[^/]+/\\.\\./", REG_EXTENDED) == 0);
initialized = 1;
}
len = strlen(s);
while (regexec(&re, s, 1, pm, 0) == 0) {
memmove(s + pm[0].rm_so, s + (pm[0].rm_eo - 1), len - pm[0].rm_eo + 2);
len -= pm[0].rm_eo - pm[0].rm_so - 1;
}
/* Replace all substrings of the form "/./" with "/" */
/*len = strlen(s);*/
for (p = s; (p = strstr(p, "/./")); ) {
memmove(p, p + 2, len - (p - s) - 1);
len -= 2;
}
return s;
}
关于C/C++中正则表达式的规则，现将opengroup.org的教程摘抄如下：（原文链接http://www.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03_06）
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The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008
Copyright © 2001-2008 The IEEE and The Open Group
9. Regular Expressions
Regular Expressions (REs) provide a mechanism to select specific strings from a set of character strings.
Regular expressions are a context-independent syntax that can represent a wide variety of character sets and character set orderings, where these character sets
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