Question

问题是要反转指向字符串的指针数组中的所有字符串。我为相同的代码编写了以下代码。显示输入的字符串后，代码无法反转字符串。我尝试将el和el2字符指针也更改为字符，但没有用。请帮助我。

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

int main() {
    int x, i, length, len, j;
    printf("How many strings you want to enter:\n");
    scanf("%d", &x);
    char *strings[x], string[50], *p, *t, *el, *el2;
    for (i = 0; i < x; i++) {
        scanf(" %49[^\n]", string);
        length = strlen(string);
        p = (char *)malloc(length + 1);
        strcpy(p, string);
        strings[i] = p;
    }
    printf("Entered strings are:\n");
    for (i = 0; i < x; i++) {
        printf("%s\n", strings[i]);
    }
    printf("Reversed strings :\n");
    for (i = 0; i < x; i++) {
        len = strlen(strings[i]);
        for (j = 0; j <= (len - 2) / 2; j++) {
            el = (strings[i] + j);
            el2 = (strings[i] + (len - j - 1));
            t = el2;
            el2 = el;
            el = t;
        }
    }
    for (i = 0; i < x; i++) {
        printf("%s\n", strings[i]);
    }
    return 0;
}

Answer 1

您正在交换局部指针变量，这毫无意义。

您需要交换指针指向的char s：

    for(j=0;j<=(len-2)/2;j++)
    {
        char t, *el, *el2;
        el = (strings[i] + j);
        el2 = (strings[i]+(len -j-1));
        t = *el2;
        *el2 = *el;
        *el = t;
    }

Answer 2

您没有更改任何内容。我建议使用交换功能：

void swap(char *a, char *b)
{
    char tmp = *a;
    *a = *b;
    *b = tmp;
}

然后进入内循环：

for(j=0;j<=(len-2)/2;j++)
{
    swap(strings[i] + j, strings[i]+(len -j-1));
}

Answer 3

在main()函数中执行字符串反转很麻烦且容易出错。相反，您应该编写一个简单的函数并使用它：

以下是经过纠正和简化的版本：

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

char *str_reverse(char *s) {
    for (size_t i = 0, j = strlen(s); i < j--; i++) {
        char t = s[i];
        s[i] = s[j];
        s[j] = t;
    }
    return s;
}

int main() {
    int x, i;

    printf("How many strings you want to enter:\n");
    if (scanf("%d", &x) != 1 || x <= 0 || x > 1000) {
        printf("Invalid number: %d\n", x);
        return 1;
    }

    char *strings[x], string[50];

    for (i = 0; i < x; i++) {
        if (scanf(" %49[^\n]", string) != 1) {
            printf("Premature end of file\n");
            return 1;
        }
        // use strdup to allocate string copies.
        // strdup is a Posix standard function
        // if your system does not have it, it is easy to implement.
        strings[i] = strdup(string);
    }
    printf("Entered strings are:\n");
    for (i = 0; i < x; i++) {
        printf("%s\n", strings[i]);
    }
    // Reverse strings
    for (i = 0; i < x; i++) {
        str_reverse(strings[i]);
    }
    printf("Reversed strings:\n");
    for (i = 0; i < x; i++) {
        printf("%s\n", strings[i]);
    }
    return 0;
}

为什么代码不反转字符串？

3 个答案: