从静态内存复制字符串到动态内存失败，程序三次输入后崩溃求助

Hey there, let's walk through exactly why your code crashes after three inputs and fix all the underlying issues. Let's start with the problems in your original code, then show a corrected version.

Key Issues in Your Original Code #

• You never use the ppFriendName parameter：This is the biggest problem! You allocate memory to byteReALL every loop, but you never save that pointer to the array passed in via ppFriendName. Each loop overwrites byteReALL, leaving the previous allocations lost (memory leak) and the caller gets nothing. No wonder the program crashes—you're not managing the intended storage at all.
• Incorrect malloc size：strlen(name) returns the length of the string without the null terminator (\0). C strings need this terminator to be valid, so you need to allocate strlen(name) + 1 bytes. Without the extra byte, you'll write past the allocated memory (buffer overflow) which causes undefined behavior like crashes.
• Misused strncpy：You're copying up to 50 bytes into byteReALL, but byteReALL only has strlen(name) bytes (which is already too small). This leads to buffer overflow, corrupting memory and causing crashes.
• Unhandled newline from fgets：fgets includes the newline character (\n) when the user presses enter. You probably don't want that in your stored names, so we should strip it.

Corrected Code #

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

void friendNamesInput(int friendNum, char **ppFriendName) {
    char name[50] = {0};
    int i = 0;

    for (i = 0; i < friendNum; i++) {
        printf("Enter name of friend %d: ", i + 1);
        // Clear any leftover newline in stdin (in case previous input left it)
        fflush(stdin);
        // Read input into name buffer
        if (fgets(name, sizeof(name), stdin) == NULL) {
            // Handle input error
            ppFriendName[i] = NULL;
            continue;
        }

        // Strip the newline character if present
        size_t nameLen = strlen(name);
        if (nameLen > 0 && name[nameLen - 1] == '\n') {
            name[nameLen - 1] = '\0';
            nameLen--;
        }

        // Allocate enough memory for the string + null terminator
        ppFriendName[i] = malloc(nameLen + 1);
        if (ppFriendName[i] == NULL) {
            // Handle allocation failure
            fprintf(stderr, "Failed to allocate memory for friend %d\n", i + 1);
            continue;
        }

        // Copy the string safely
        strcpy(ppFriendName[i], name);
    }
}

// Example usage
int main() {
    int numFriends = 3;
    // First allocate an array of char pointers to hold each name
    char **friendNames = malloc(numFriends * sizeof(char*));
    if (friendNames == NULL) {
        fprintf(stderr, "Failed to allocate pointer array\n");
        return 1;
    }

    friendNamesInput(numFriends, friendNames);

    // Print the names to verify
    printf("\nYour friends' names:\n");
    for (int i = 0; i < numFriends; i++) {
        if (friendNames[i] != NULL) {
            printf("%d: %s\n", i + 1, friendNames[i]);
            // Don't forget to free each name when done!
            free(friendNames[i]);
        }
    }
    // Free the pointer array itself
    free(friendNames);
    return 0;
}

What Changed & Why #

• Used ppFriendName[i] to store each allocated pointer: Now each name is saved to the array passed in, so the caller can access them.
• Fixed malloc size: We allocate nameLen + 1 to make space for the null terminator.
• Stripped the newline: Makes the stored names clean without the extra \n.
• Added error handling: Checks for fgets failure and malloc failure to avoid crashes from unexpected issues.
• Added example main function: Shows how to properly allocate the pointer array before calling the function, and how to free all memory to avoid leaks.

内容的提问来源于stack exchange，提问作者user6721998