模拟strcpy的C代码运行出现Bus Error，请求排查错误原因

Hey there! Let's break down why you're running into a Bus Error with your custom strcpy function, and how to fix it.

First, a quick recap: Bus Errors often pop up when your program tries to access memory in an invalid way—this could be writing to read-only memory, accessing unallocated memory, or hitting misaligned memory addresses (though that's less common in string operations like this).

Let's start with the most likely causes in your case: #

• Writing to read-only memory
  If you're calling ft_strcpy with a string literal as the dest parameter (like ft_strcpy("my_string", "source")), you're trying to write to a read-only section of memory where string literals are stored. Most operating systems protect this space, so attempting to modify it triggers a Bus Error.

• Using an invalid dest pointer
  If dest is NULL, an uninitialized pointer, or points to memory that hasn't been allocated (e.g., you forgot to call malloc), accessing dest[index] will try to read/write to a non-existent or restricted memory address—boom, Bus Error.

• Insufficient space in dest
  If dest doesn't have enough room to hold the entire src string (including the terminating \0), you'll write past the end of the allocated memory. This can corrupt other data or trigger a Bus Error/Segmentation Fault when accessing out-of-bounds memory.

Quick fix for your code first: #

I notice your ft_strcpy cuts off at dest[index] =...—you need to add dest[index] = '\0'; at the end to properly terminate the copied string. Without this, functions like ft_putstr will keep reading past the end of the string, leading to more undefined behavior.

Example of correct vs. incorrect calls: #

❌ Bad calls that cause Bus Errors:

// 1. Writing to a read-only string literal
ft_strcpy("hello", "world");

// 2. Using a NULL pointer as dest
char *dest = NULL;
ft_strcpy(dest, "test");

// 3. dest is too small for src
char dest[3];
ft_strcpy(dest, "hello"); // src has 5 chars + 1 null terminator = 6 bytes needed

✅ Good calls that work safely:

// 1. Using a stack-allocated array with enough space
char dest[20];
ft_strcpy(dest, "hello world");

// 2. Using dynamically allocated memory
#include <stdlib.h>
#include <string.h>

char *src = "hello world";
char *dest = malloc(strlen(src) + 1); // +1 for the null terminator
if (dest != NULL) {
    ft_strcpy(dest, src);
    ft_putstr(dest);
    free(dest); // Don't forget to free allocated memory!
}

How to debug this further: #

• Print out the values of dest and src before calling ft_strcpy to make sure dest points to valid, writable memory.
• Use a debugger (like gdb) to step through your code—this will let you see exactly which line triggers the Bus Error, and check the state of your pointers at that moment.

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