从 C 中的字符串中删除子字符串 [英] Remove a substring from a string in C

问题描述

我想从字符串中删除一个特定的子字符串，例如我的主字符串是 "ababccdabce" 并且我想从中删除 "abc" 以便它将变成 "abcde".

I want to remove a particular substring from a string for example my main string is "ababccdabce" and I want to remove "abc" from it so it will become "abcde".

我只是想知道 C 中是否有一个预定义的函数可以做到这一点，如果没有，该怎么做?

I just wanted to know if there is a predefined function in C to do that, and if not, how to do it?

推荐答案

C 中没有预定义的函数可以从 C 字符串中删除给定的子字符串，但您可以使用 strstr 和 <代码>记住.请注意，如果您原地删除子字符串，则不能使用 memcpy 或 strcpy，因为如果源数组和目标数组重叠，它们将具有未定义的行为.

There is no predefined function in C to remove a given substring from a C string, but you can write one using strstr and memmove. Note that if you remove the substring in place, you cannot use memcpy nor strcpy because these have undefined behavior if the source and destination arrays overlap.

代码如下:

#include <string.h>

char *strremove(char *str, const char *sub) {
    size_t len = strlen(sub);
    if (len > 0) {
        char *p = str;
        while ((p = strstr(p, sub)) != NULL) {
            memmove(p, p + len, strlen(p + len) + 1);
        }
    }
    return str;
}

请注意，结果字符串可能包含子字符串，就像您的示例一样.

Note that the resulting string may contain the substring as is the case in your example.

Netherwire 提出了优化建议:

char *strremove(char *str, const char *sub) {
    size_t len = strlen(sub);
    if (len > 0) {
        char *p = str;
        size_t size = 0;
        while ((p = strstr(p, sub)) != NULL) {
            size = (size == 0) ? (p - str) + strlen(p + len) + 1 : size - len;
            memmove(p, p + len, size - (p - str));
        }
    }
    return str;
}

进一步磨练代码，我想出了一个使用 2 指法的更有效的版本:只在第一场比赛之后开始复制比赛之间的片段:

Further honing the code, I came up with an even more efficient version using the 2 finger-method: only copying the fragments between matches starting after the first match:

char *strremove(char *str, const char *sub) {
    char *p, *q, *r;
    if (*sub && (q = r = strstr(str, sub)) != NULL) {
        size_t len = strlen(sub);
        while ((r = strstr(p = r + len, sub)) != NULL) {
            memmove(q, p, r - p);
            q += r - p;
        }
        memmove(q, p, strlen(p) + 1);
    }
    return str;
}

这里是相同的方法，没有调用 memmove:

Here is the same method without any calls to memmove:

char *strremove(char *str, const char *sub) {
    char *p, *q, *r;
    if (*sub && (q = r = strstr(str, sub)) != NULL) {
        size_t len = strlen(sub);
        while ((r = strstr(p = r + len, sub)) != NULL) {
            while (p < r)
                *q++ = *p++;
        }
        while ((*q++ = *p++) != '\0')
            continue;
    }
    return str;
}

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