编写实现两个字符串交替写入及迭代首尾改写的C程序问询

Here's a complete C program that meets your requirement of alternatingly writing two strings into an initial "X-filled" buffer, replacing characters from the start and end in each iteration until the entire buffer is rewritten. I’ll break down how it works step by step.

Full Code #

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

int main() {
    // Define your two input strings (modify these as needed)
    const char *str1 = "I like ";
    const char *str2 = "programming!";
    
    // Calculate total buffer length using strlen() as required
    int len1 = strlen(str1);
    int len2 = strlen(str2);
    int total_length = len1 + len2;
    
    // Allocate buffer and initialize with 'X's
    char *buffer = (char *)malloc(total_length + 1);
    if (buffer == NULL) {
        perror("Failed to allocate memory");
        return 1;
    }
    memset(buffer, 'X', total_length);
    buffer[total_length] = '\0'; // Null-terminate the string
    
    int left_ptr = 0;       // Pointer starting at the buffer's start
    int right_ptr = total_length - 1; // Pointer starting at the buffer's end
    int idx1 = 0;           // Traverse str1 left-to-right
    int idx2 = len2 - 1;    // Traverse str2 right-to-left
    
    printf("Initial buffer: %s\n", buffer);
    
    // Alternate replacing 'X's from both ends
    while (left_ptr <= right_ptr && (idx1 < len1 || idx2 >= 0)) {
        // Replace leftmost 'X' with next character from str1
        if (idx1 < len1) {
            buffer[left_ptr] = str1[idx1];
            left_ptr++;
            idx1++;
            printf("After left replacement: %s\n", buffer);
        }
        
        // Replace rightmost 'X' with next character from str2 (if space remains)
        if (idx2 >= 0 && left_ptr <= right_ptr) {
            buffer[right_ptr] = str2[idx2];
            right_ptr--;
            idx2--;
            printf("After right replacement: %s\n", buffer);
        }
    }
    
    // Show the final complete string
    printf("\nFinal completed string: %s\n", buffer);
    
    // Clean up allocated memory
    free(buffer);
    return 0;
}

Key Details & Explanation #

• Buffer Setup: We calculate the total required buffer length by adding the lengths of both input strings (using strlen() as specified). The buffer is dynamically allocated to work with any string lengths, then filled entirely with 'X's using memset().
• Dual Traversal: We use two pointers to track where to replace 'X's—one starting at the left (for str1) and one at the right (for str2). We traverse str1 from start to end, and str2 from end to start to match your alternating rewrite requirement.
• Iterative Replacement: In each loop iteration, we first replace the leftmost available 'X' with a character from str1, print the buffer, then replace the rightmost available 'X' with a character from str2, and print again. This continues until all characters are written or the pointers meet in the middle.
• Memory Safety: We check for allocation failures and free the buffer at the end to avoid memory leaks.

Sample Output #

Running this program will produce output matching your example’s pattern:

Initial buffer: XXXXXXXXXXXXXXXXXXX
After left replacement: IXXXXXXXXXXXXXXXXXX
After right replacement: IXXXXXXXXXXXXXXXX!
After left replacement: I XXXXXXXXXXXXXXXX!
After right replacement: I XXXXXXXXXXXXXXXg!
After left replacement: I lXXXXXXXXXXXXXXg!
After right replacement: I lXXXXXXXXXXXXXng!
...
Final completed string: I like programming!

内容的提问来源于stack exchange，提问作者user8310120