C language implementation Four ways to return string functions _c language

Objective

There are four ways to return string functions in the C language, respectively:

1. Use heap space, return the heap address of the application, pay attention to release
2. function parameter passes the pointer and returns the pointer
3. Returns the static variables defined within a function (shared)
4. Return global variable
   

Let's take a look at the detailed introduction

In fact, to return a valid pointer, the tail variable is invalid after exiting.

Use allocated memory, address is valid

Char *fun () 
{ 
  char* s = (char*) calloc (M, sizeof (char*)); 
  if (s) 
    strcpy (S, "abc"); 
  return s; 

But this approach needs to be noted, and must be free from using the address that will be returned

The address is passed into the

char* Fun (char*s) 
{ 
  if (s) 
    strcpy (S, "abc"); 
  return s; 

This way call should be aware that the size assigned to S is sufficient.

You can do this:

char* Fun (char*s, int len) 
{ 
  if (s) 
  { 
    strncpy (s, ABC, len-1); 
    S[len-1] = 0; 
  } 
  return s; 

or use local static variables

char* Fun () 
{ 
  static char s[100]; 
  strcpy (S, "abc"); 
  return s; 

This approach requires attention, do not modify the returned string, because it is a shared address, changes to it will be reflected to each caller. You can do this:

Const char* Fun () 
{ 
  static char s[100]; 
  strcpy (S, "abc"); 
  return s; 

There is also a use of global variables

Char g_s[100]; 
char* Fun () 
{ 
  strcpy (g_s, "abc"); 
  return s; 

Also, be aware of the maximum space that this variable can store.

Summarize

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