如何解决如何使用 C 正则表达式提取子匹配
我已经使 GNU 正则表达式库完全按照我大约 2 年前写的广泛文本处理算法中所宣传的那样工作,但不幸的是该平台已经消失,我不知道它的版本是否比下面引用的版本旧或新.
代码如下:
// GNU libc version: 2.28
// gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
#include <stdio.h>
#include <regex.h>
int main() {
regex_t preg;
char str[] = "dave";
char regex[] = "\\(.\\)ave";
// flag REG_EXTENDED with unescaped parens in the r.e. doesn't fix anything
int ret,cflags = REG_ICASE;
// the elements of unused pmatches used to be set to -1 by regexec,but no longer. a clue perhaps.
regmatch_t pmatch[2] = {{-1,-1},{-1,-1}};
ret = regcomp(&preg,regex,cflags);
if (ret) {
puts("regcomp fail");
return ret;
}
else
// preg.re_nsub contains the correct number of groups that regcomp recognized in the r.e. Tests succeeded for 0,1,2,and 3 groups.
printf("regcomp ok; re_nsub=%zu\n",preg.re_nsub);
ret = regexec(&preg,str,pmatch,0);
if(ret)
puts("no match");
else {
printf("match offsets are %d %d\n",pmatch[0].rm_so,pmatch[0].rm_eo);
printf("match[0]=%*s<\n",pmatch[0].rm_eo,&str[pmatch[0].rm_so]);
printf("submatch offsets are %d %d\n",pmatch[1].rm_so,pmatch[1].rm_eo);
if(pmatch[1].rm_so != -1)
printf("match[1]=%*s<\n",pmatch[1].rm_eo,&str[pmatch[1].rm_so]);
}
return 0;
}
/*
output:
regcomp ok; re_nsub=1
match offsets are 0 4
match[0]=dave<
submatch offsets are -1 -1
*/
解决方法
您没有获得第一个捕获组的偏移量的问题是您将 1
作为第三个 size_t __nmatch
参数传递给 regexec
。
1
值应更改为 2
,因为每当 \(.\)ave
正则表达式匹配时都会有两个组:第 0 组将保存整个匹配,第 1 组将保存第一次捕获群体价值。
所以,你需要使用
ret = regexec(&preg,str,2,pmatch,0);
// ^^^
此外,要打印您可以使用的第 1 组值
if(pmatch[1].rm_so != -1) {
printf("match[1]=%.*s<\n",pmatch[1].rm_eo,&str[pmatch[1].rm_so]);
}
#include <stdio.h>
#include <regex.h>
#include <string.h>
int main() {
regex_t preg;
char str[] = "dave";
char regex[] = "\\(.\\)ave";
// flag REG_EXTENDED with unescaped parens in the r.e. doesn't fix anything
int ret,cflags = REG_ICASE;
// the elements of unused pmatches used to be set to -1 by regexec,but no longer. a clue perhaps.
regmatch_t pmatch[2] = {{-1,-1},{-1,-1}};
ret = regcomp(&preg,regex,cflags);
if (ret) {
puts("regcomp fail");
return ret;
}
else
// preg.re_nsub contains the correct number of groups that regcomp recognized in the r.e. Tests succeeded for 0,1,and 3 groups.
printf("regcomp ok; re_nsub=%zu\n",preg.re_nsub);
ret = regexec(&preg,0); // 1 changed to 2 as there is Group 0 (whole match) and Group 1 (for the first capturing group)
if(ret)
puts("no match");
else {
printf("match offsets are %d %d\n",pmatch[0].rm_so,pmatch[0].rm_eo);
printf("match[0]=%*s<\n",pmatch[0].rm_eo,&str[pmatch[0].rm_so]);
printf("submatch offsets are %d %d\n",pmatch[1].rm_so,pmatch[1].rm_eo);
if(pmatch[1].rm_so != -1) {
printf("match[1]=%.*s<\n",&str[pmatch[1].rm_so]);
}
}
return 0;
}
/*
regcomp ok; re_nsub=1
match offsets are 0 4
match[0]=dave<
submatch offsets are 0 1
match[1]=d<
*/
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