strcasestr仍然无法正常工作

所以我通读了其他问题,他们被告知在任何包含之前放#define _GNU_SOURCE它会起作用,但它对我不起作用.我也尝试添加#define _GNU_SOURCE char * strcasestr(const char * haystack,const char * needle);但仍然无法正常工作.我找不到任何其他相关信息,也许任何人都可以提供帮助?提前致谢.

错误:函数’strcasestr’的隐式声明

/**
 *
 * Description:  This is code for Lab 3 Task 2.
 *               Reads data from file and gives opportunity to search by cities
 */
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

    printf("Please input the city you want to find employees in:");
    scanf("%s", input);
    maxline = i;
    for (i = 0; i <= maxline; i++) {
        if (strcasestr(employee[i].city, input) != 0) { // PROBLEM
            printf("%d %s %s %s\n", &employee[i].ID, employee[i].fn,
                                    employee[i].ln, employee[i].city);
            amount++;
        }
    }
    printf("%d matches out of %d members", amount, maxline);
    return 0;
}

最佳答案 strcasestr函数不可用作标准Windows构建环境的一部分.它不是C标准库的一部分,只与某些平台和构建环境一起发布.

但是,您可以编写自己的版本.这是一个基于天真字符串匹配算法的简单方法.您可以使用Rabin-Karp,Boyer-Moore或Knuth-Morris-Pratt算法做得更好:

char* myStrcasestr(const char* haystack, const char* needle) {
    /* Edge case: The empty string is a substring of everything. */
    if (!needle[0]) return (char*) haystack;

    /* Loop over all possible start positions. */
    for (size_t i = 0; haystack[i]; i++) {
        bool matches = true;
        /* See if the string matches here. */
        for (size_t j = 0; needle[j]; j++) {
            /* If we're out of room in the haystack, give up. */
            if (!haystack[i + j]) return NULL;

            /* If there's a character mismatch, the needle doesn't fit here. */
            if (tolower((unsigned char)needle[j]) != 
                tolower((unsigned char)haystack[i + j])) {
                matches = false;
                break;
            }
        }
        if (matches) return (char *)(haystack + i);
    }
    return NULL;
}
点赞