C语言中使用while循环反转字符串的代码问题求助

Hey there! Let's walk through what's off with your current code and how to fix it, plus clarify how to work with the char* s parameter.

First: Understanding the char* s Parameter #

In C, a string is a null-terminated ('\0') array of characters. The char* s parameter is a pointer that points to the first character of this string. You can use it two ways:

• Like an array: s[0] gives the first character, s[1] the second, etc.
• As a pointer you can increment/decrement: s++ moves the pointer to the next character, s-- moves it back.

Important note: If you pass a string literal (like "hello") directly to this function, you can't modify it (they're stored in read-only memory). Always use a mutable character array (like char myStr[] = "abc de fgh";) when calling this reversal function.

What's Wrong With Your Current Code? #

Let's break down the bugs one by one:

1. Incorrect pointer initialization:
   • char* i = 0; sets i to a null pointer (not the start of the string). You need char* i = s; to point to the first character of the input string.
   • char* j = strlen(s)-1; tries to assign an integer to a pointer. You need to calculate the address of the last valid character: char* j = s + strlen(s) - 1; (since strlen(s) gives the length of the string, adding that to s points past the last character, so subtract 1 to get the last actual character before '\0').
2. Wrong swap logic:
   • char* temp; declares a pointer, but you need to swap the character values (not the pointers themselves). So temp should be a char variable, not a pointer.
   • Your current code swaps the pointers i and j instead of the characters they point to. This doesn't modify the original string at all—you're just moving where the pointers point, not changing the string's content.

Fixed Code #

Here's the corrected version of your function, with comments explaining each step:

#include <string.h> // Required for strlen()

void stringReverse(char* s) {
    // Point i to the start of the string
    char* i = s;
    // Point j to the last valid character (before the null terminator '\0')
    char* j = s + strlen(s) - 1;
    // Temp variable to hold a character during the swap
    char temp;

    // Swap characters while i is positioned before j
    while (i < j) {
        // Save the character at i's position to temp
        temp = *i;
        // Copy the character at j's position to i's position
        *i = *j;
        // Copy the saved character from temp to j's position
        *j = temp;
        // Move i forward one character
        i++;
        // Move j backward one character
        j--;
    }
}

How to Use This Function #

Here's an example of calling it in a main function to test the reversal:

#include <stdio.h>

int main() {
    // Use a mutable character array (not a string literal) so we can modify it
    char str[] = "abc de fgh";
    printf("Original string: %s\n", str);
    stringReverse(str);
    printf("Reversed string: %s\n", str);
    return 0;
}

This will output:

Original string: abc de fgh
Reversed string: hgf ed cba

Key Takeaways #

• Always initialize pointers to valid memory locations (not 0 unless you explicitly mean a null pointer).
• When modifying string content, work with the values pointed to by the pointers (using *pointer syntax), not the pointers themselves.
• Remember that string literals are read-only—use character arrays if you need to modify the string's content.

内容的提问来源于stack exchange，提问作者user11361420