What is the different between Strcpy and strdup in C?

The Difference Between strcpy and strdup

1. Definition and Functionality

• strcpy(): This is a function in the standard C library used to copy a string to another string. Its prototype is char *strcpy(char *dest, const char *src);, which copies the string pointed to by src to the address pointed to by dest, including the null terminator '\0'.

• strdup(): This is not part of the standard C library and is typically implemented in POSIX systems. Its function is to copy a string while allocating memory using malloc, so the user must free the memory using free() after the string is no longer needed. The function prototype is char *strdup(const char *s);, which returns a pointer to a new string that is a complete copy of the original string s.

2. Memory Management

• strcpy() requires the user to pre-allocate sufficient memory to store the destination string. This means the user must ensure that the memory space pointed to by dest is large enough to accommodate the string being copied; otherwise, it may cause buffer overflow, leading to security vulnerabilities.

• strdup() automatically allocates memory for the copied string (using malloc), so the user does not need to pre-allocate memory. However, this also means the user is responsible for freeing this memory (using free()) to avoid memory leaks.

3. Use Cases

• strcpy() Use Case:

  c
  char src[] = "Hello, world!";
  char dest[50];  // Allocate sufficient memory
  strcpy(dest, src);
  printf("Copied string: %s\n", dest);

• strdup() Use Case:

  c
  char src[] = "Hello, world!";
  char *dest = strdup(src);
  if (dest != NULL) {
      printf("Duplicated string: %s\n", dest);
      free(dest);  // Remember to free memory after duplication
  } else {
      printf("Memory allocation failed\n");
  }

4. Summary

Choosing between strcpy() and strdup() depends on specific requirements and context:

• If pre-allocated memory is available or more control over memory management is needed, strcpy() is a good choice.
• If simplifying memory management is desired and it is acceptable to use a non-standard function while properly freeing the memory, strdup() is a more convenient choice.

When using these functions, it is essential to adhere to security best practices and memory management guidelines to avoid introducing vulnerabilities and memory issues.