Memory Allocation in C

The memory occupied by a C program can be divided into the following categories:  (1) Stack  This is the region automatically allocated and released by the compiler. It mainly stores function parameters and local variables of functions. When a function starts to execute, partial variables are pushed into the stack for the real parameters required by the function. After the function is executed, parameters and variables that have previously entered the stack are also released. Its running mode is similar to the stack in the data structure.  (2) Heap  This is a region controlled by programmers for allocation and release. In C, the space allocated by using the malloc () function exists on the stack. The space allocated on the stack is not automatically released after a function is executed like the stack, but exists throughout the running of the program. Of course, if you do not manually release (free () function) these spaces, the system will automatically release them after the program runs. For small programs, the impact may not be felt, but for large programs, such as a large game, there will be a problem of insufficient memory.  (3) Global Zone  The global variables and static variables in C are stored in the global zone. They are a bit like the space on the stack, and they also exist continuously.  But the difference is that they are allocated and released by the compiler itself.  (4) text Constant Area  For example, if char * c = "123456", "123456" is a text constant, which is stored in the text constant area. It is also controlled by the compiler for allocation and release.  (5) code area  Stores the binary code of the function body.  2. Example (1)  Int A = 0; // global Zone Void main () { Int B; // Stack Char s [] = "ABC"; // s in the stack, "ABC" in the text Constant Area Char * P1, * P2; // Stack Char * P3 = "123456"; // "123456" in the constant area, P3 in the stack Static int C = 0; // global Zone P1 = (char *) malloc (10); // P1 is on the stack, and the allocated 10 bytes are on the heap  P2 = (char *) malloc (20); // P2 on the stack, 20 bytes allocated in the heap  Strcpy (P1, "123456"); // put "123456" in the constant area  // The Compiler may optimize it to the "123456" that P3 points. }  3. Example (2)  // Returns the char pointer.  Char * F ()  {  // The s array is stored on the stack.  Char s [4] = {'1', '2', '3', '0 '};  Return s; // return the address of the S array, but the S array is released after the program runs.  }  Void main () { Char * s;  S = f ();  Printf ("% s", S); // print out garbled characters. Because s points to the address, there is no data  }