C Four functions of language memory management

1、malloc function

grammar ：malloc（ You need to apply for the size of memory space ）, Default return void* Type pointer , But for convenience , When returning, convert the type

char * ptr;
ptr = (char *)malloc(sizeof(char)*4);

because malloc Function will not help you initialize the requested space , So you need to initialize yourself , You can also use （string.h） Library function memset(void*,void,sizeof（）) For initialization, you can also use

2、calloc function

Syntax and malloc Exactly the same as , The only difference is calloc Will be initialized automatically , The number is initialized to 0, Characters are initialized to spaces by default

char * ptr;
ptr = (char *)calloc(sizeof(char)*4);

When the space of your first application is insufficient, you need to apply for a second time and copy the data of the first time string.h） Library function memcpy(void*,void*,int) Of course, you can also use

3、realloc function

This function can be understood as adding x Data , You need it. realloc（ptr, Original number +x）, The original data remains unchanged

char * ptr;
ptr = (char *)malloc(sizeof(char)*2);
// Yes ptr Carry out a series of operations 
ptr = (char *)realloc(ptr,sizeof(char)*4);

4、free function

grammar ：void free(void *ptr);

char * ptr;
ptr = (char *)malloc(sizeof(char)*4);
free(ptr);

Memory leak problem

1、 Implicit memory leaks ：malloc The application memory is not released in time after it is used up
2、 Missing memory block address ： Point the unique pointer to a memory block to another address , There was no one at that address until where , It can't be released
To avoid memory leaks ,malloc（ Such as the function of applying for space ） And free Functions appear in pairs