[C++] Dynamic memory management ① (Dynamic memory management in C language | C language memory application | C language memory release | Code examples)

1. Dynamic memory management

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Dynamic memory management is provided by

• Memory application
• memory release

Composition, the memory here refers to heap memory, as opposed to stack memory;

During program running, dynamic memory management is often performed as needed to more flexibly manage memory resources, including:

• Allocate memory space in heap memory
• Release memory space in heap memory

In C language and C++ language, there are methods to dynamically allocate/release heap memory;

• In C language, it mainly involves the allocation and release of heap memory;
• In the C++ language, the main thing is the dynamic creation and release of objects;

2. Dynamic memory management in C language

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1. C language memory application

In C language, use standard library functions such as malloc(), calloc(), realloc() and so on to dynamically apply for memory:

• malloc(size_t size): Allocate heap memory of the specified byte size, return a pointer to the heap memory space, or return NULL on failure;
• calloc(size_t num, size_t size): Allocate heap memory with the specified number of blocks and byte size. Compared with malloc, calloc automatically initializes the memory to 0;
• realloc(void* ptr, size_t size): Modify the byte size of the allocated memory block; if the pointer parameter ptr is NULL, this function has the same function as the malloc function; if the parameter size is 0, this function has the same function as the free function , used to release ptr memory;

Before calling the above function, you need to import the stdlib.h header file;

#include <stdlib.h>  

2. C language memory release

In C language, call the free() standard library function to release the allocated memory;

3. Code example - C language dynamic memory management

In the code below,

First, use the malloc() function to dynamically apply for heap memory that can store 5 int data.

// 函数原型 : 
void *malloc(unsigned int size)；

Then, convert the void * type pointer returned by the malloc function into an int * type pointer;

// 函数原型 : 
// void *malloc(unsigned int size)；
// 申请内存
int* array = (int*)malloc(5 * sizeof(int));

Then, use array subscripts to access the memory and assign values ​​to the memory;

    // 为内存赋值
    // 赋值时使用数组下标的方式访问内存
    for (int i = 0; i < 5; i++) {
    
    
        array[i] = i;
    }

Then, print the memory data and use pointers to access the memory when obtaining the memory space value;

    // 打印内存
    // 获取内存空间值时使用指针形式访问内存
    for (int i = 0; i < 5; i++) {
    
    
        printf("%d ", *(array + i));
    }

Finally, call the free function to release this memory;

    // 释放内存  
    free(array);

Code example:

#include <stdio.h>  
#include <stdlib.h>  

int main() {
    
    
    // 申请内存
    int* array = (int*)malloc(5 * sizeof(int));
    if (array == NULL) {
    
    
        printf("内存分配失败\n");
        return -1;
    }

    // 为内存赋值
    // 赋值时使用数组下标的方式访问内存
    for (int i = 0; i < 5; i++) {
    
    
        array[i] = i;
    }

    // 打印内存
    // 获取内存空间值时使用指针形式访问内存
    for (int i = 0; i < 5; i++) {
    
    
        printf("%d ", *(array + i));
    }
    printf("\n");

    // 释放内存  
    free(array);

    // 控制台暂停 , 按任意键继续向后执行
    system("pause");

    return 0;
}

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