问号(?)在regex中不工作

I was trying to write a simple c program to check if a path name has a ".jpg" or ".jpeg" suffix. Here is my program:

我试图编写一个简单的c程序来检查路径名是否有“.jpg”或“.jpeg”后缀。这是我的计划:

#include <stdio.h>
#include <string.h>
#include <regex.h>

regex_t regex;

static int is_acceptable_format(const char *path) {
    int reti = regexec(&regex, path, 0, NULL, 0);

    if (!reti) {
        return 1;
    } else if (reti == REG_NOMATCH) {
        return 0;
    } else {
        char msgbuf[100];
        regerror(reti, &regex, msgbuf, sizeof(msgbuf));
        printf("Regex match failed: %s\n", msgbuf);

        return 0;
    }
}

static void init_accpetable_format() {
    if (regcomp(&regex, "\\.JP(E?)G$", REG_ICASE)) {
        printf("Could not compile regex\n");
    }
}

main()
{
    const char *path = "/sample_img.jpg";
    init_accpetable_format();
    printf("path=\"%s\" is %s\n",
        path, is_acceptable_format(path) ? "acceptable" : "unacceptable");
}

I expected my program to return "acceptable" but it returned "unacceptable" instead. If I make my regex be "\.JPG$", the result became "acceptable".

我希望我的程序可以返回“可接受的”，但它却返回“不能接受”。如果我将regex设置为“\”。JPG$，结果变得“可接受”。

I thought question mark (?) in regex means 0 or 1 times regex rule. But why doesn't it work?

我认为在regex中问号(?)的意思是0或1乘以regex规则。但是为什么它不工作呢?

1 个解决方案

#1

? is part of the extended POSIX regexes, not the basic POSIX regex: http://en.wikipedia.org/wiki/Regular_expression#POSIX_basic_and_extended

吗?是扩展POSIX regexes的一部分，而不是基本的POSIX regex: http://en.wikipedia.org/wiki/Regular_expression#POSIX_basic_and_extended吗

As such, you need to add the flag REG_EXTENDED to your regexcomp, like in this example : http://www.lemoda.net/c/unix-regex/

因此，您需要在regexcomp中添加标记REG_EXTENDED，比如在这个示例中:http://www.lemoda.net/c/unix regex/。

#1