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This article mainly shows you the "example Analysis of dynamic memory in C language", which is easy to understand and clear. I hope it can help you solve your doubts. Let me lead you to study and learn the article "sample Analysis of dynamic memory in C language".

1. Functions on dynamic memory 1.1 malloc and free functions

Malloc this function requests a continuously available space from memory and returns a pointer to this space. If it is opened successfully, it returns a pointer to open up a good space; if it fails, it returns a NULL pointer, so the return value of malloc must be checked.

The free function is specifically used to release and reclaim dynamic memory. If the space pointed to by the parameter ptr is not dynamically opened, the behavior of the free function is undefined; if the parameter ptr is a NULL pointer, the function does nothing.

Description:

The ingenious design of this function is that the return value is void*, because the function creator does not know what type pointer the user wants to receive the dynamically opened space, so the user only needs to forcibly convert it to the type he wants when using it:

Int* p = (int*) malloc (40); / / an example of assuming it is an integer

After using the dynamically opened space, remember to use the free function to release the open space to the operating system, and assign the pointer to a null pointer:

Int* p = (int*) malloc (40); / / Free (p); / / avoid memory leaks p = NULL;// since the location of the original pointer has been returned to the operating system, assign the pointer to a null pointer to avoid problems such as wild pointers

If the parameter size is 0malloc, the behavior is standard and undefined, depending on the compiler.

Header file stdlib.h is required

1.2 calloc function

Calloc can be compared with the malloc function, which opens up a space for num elements of size size and initializes each byte of the space to 0. It is different from malloc in two ways:

Parameters are different, calloc needs to specify the data type that opens up the space and the number of data of that type, while malloc is the total number of bytes

While opening up the space, calloc initializes all bytes in the space to 0. 0.

1.3The realloc function

The realloc function is used to adjust the size of the opening space, sometimes the space may be smaller, sometimes it may be larger, it can be modified by the realloc function, and the data in the original memory will be moved to a new space.

Realloc has two situations when resizing space:

There is enough space behind the original space. In this case, the extended memory will append the space directly after the original memory. The data of the original space will not change, and the return value will be the pointer of the original location.

two。 If there is not enough space behind the original space, we will find a suitable size of continuous space in the heap space, and transfer the data of the original space to the new space and return the address of the new space.

Int main () {int* str = (int*) malloc (10); if (str! = NULL) {/ /.} else {exit (EXIT_FAILURE);} / expand capacity / / Code 1str = (int*) realloc (str, 1000); / / is that okay? (a null pointer will be returned if the application fails!) / / modify the code 2int*p = NULL;p = realloc (str, 1000); if (p! = NULL) {str = p;} /. Free (str); return 0;} 2. Common dynamic memory errors 2. 1 dereferencing NULL pointers int* p = (int*) malloc (40);

This ignores the possibility that the return value may be a null pointer, which will be returned if the opening fails. So the best thing to do is to determine whether the pointer is empty or not before moving on to the next step.

Int* p = (int*) malloc (40); if (p! = NULL) {* paired 10;} free (p); 2.2 Spatial out-of-bounds access to dynamic memory

It is similar to cross-boundary access to an array when using an array.

Int iTun0; int * p = (int *) malloc (10*sizeof (int)); if (NULL = = p) {exit (EXIT_FAILURE);} for (iTuno; I

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