Ii. dynamic memory allocation and use

Ii. dynamic memory allocation and use
1. malloc (1) malloc allocation function: requires the size of the requested space (in bytes) (2) the returned value is a first address, which is received by a pointer (3) use sizeof to calculate the element size (4) use the malloc function to apply for memory space, which needs to be released after use; otherwise, memory leakage may occur (5) release function free needs to point to the allocated memory pointer (6) basic Format: void * malloc (unsigned int size); (7) Allocate the specified memory size, but do not clear the allocated space 0 (8) free (pointer ); // release heap space, Mark deletion, unclear content (9) Example: ① malloc and one-dimensional array "1" to add square brackets, pointers, two transformations of arrays, regardless of the dimension array, several * can generate 10 integers randomly in "2" and save them to the heap zone int * parr = malloc (sizeof (int) * 10 ); // create 10 integer spaces in the heap area for (int I = 0; I <10; I ++) {parr [I] = arc4random () % (100-10 + 1) + 10; // generates 10 random numbers [10,100]
} For (int I = 0; I <10; I ++) {printf ("% d", parr [I]); // output
} Printf ("\ n"); // line feed free (parr ); // release the Applied Space ② malloc and the two-dimensional array 1 allocate two rows and three columns of the Two-dimensional array 2 int (* pa) [3] = malloc (sizeof (int) * 2*3); int (* pa) [3] = malloc (sizeof (int) * 2*3 ); // create a 2-row, 3-column integer space pa [0] [0] = 1; // assign a value of pa [0] [1] = 13; ③ malloc and string "1" Save the string "Hello, Lanou" to heap area solution 1: char * pst = malloc (sizeof (char) * 12 ); // open up 12 char-type spaces. Note the \ 0 strcpy (pst, "Hello, Lanou") at the end of the string; // copy the string printf ("% s \ n ", pst); // output free (pst); // release memory solution 2: char a [] = "Hello, Lanou "; // copy the string char * ps = malloc (sizeof (a) in the constant area in the stack area; // open the strcpy (ps, a) space of the string size ); // copy the string in the stack area to the free (ps) in the stack area; // release the memory ④ malloc and the string array 1 char (* p) [255] = malloc (5*255); // open up 5 strings, each string contains 255 bytes of space "2" strcpy (p [0], "iPhone "); // copy the string to the first string array ⑤ malloc and the struct typedef struct person {// create a struct char name [20] with two elements; int age;
} Person; solution 1: int main () {Person * pp = malloc (sizeof (Person); // open a space strcpy (pp-> name, ""); // string copy, value: printf ("% s \ n", pp-> name); // output pp-> age = 34; // integer value: printf ("% d \ n", pp-> age); // output free (pp); // release memory} solution 2: person p = {"baye", 20}; // assign the initial value Person * pi = malloc (sizeof (Person) to the struct based on the features that struct values can be directly assigned )); // open up a space * pi = p for the size of the struct; // directly copy all the values of the struct in the stack area to the pi 6 malloc in the stack area and the pointer of the struct array "1" Using arrows, the struct array uses the struct array of three elements in "2". solution 1: Person * pt = malloc (sizeof (Person) * 3 ); // create three strcpy spaces (pt [0]. name, "Lanou"); // (pt + 0)-> name), copy the string pt [0]. age = 10; // assign printf ("% s \ n", pt [0] to an element of the first struct of the struct array. name); // output free (pt); // release memory solution 2: Person pt [3] = {"erdanzi", 23}, {"bee ", 20 },{ "liuwa", 30 }}; Person * pp = malloc (sizeof (Person) * 3); for (int I = 0; I <3; I ++) {pp [I] = pt [I]; // values can be directly assigned between structures.
} For (int I = 0; I <3; I ++) {printf ("% s % d \ n", pp [I]. name, pp [I]. age );
} Free (pp); // release memory 2. other memory allocation functions ① calloc 1 void * calloc (unsigned n, unsigned size ); 2. Use free to release 3 and allocate n size Space 4. Unlike malloc, the memory space applied for by calloc is initialized to 0 and 5 is not recommended, this vulnerability may cause access to the Internet. The C language does not provide cross-border protection. Programmers need to check cross-border protection. ② realloc void * realloc (void *, unsigned newSize) 2. Use free to release 3 and reassign 4 from small to large based on the given address and size. data will not be lost from large to small, example of data loss: // The original allocated space int * p = malloc (100); // The allocated space p = realloc (p, 150); 3. memory Operation Function ① meset void * memset (void * s, int c, size_t n); 2 is not only used in heap zone, it is also used to start with Stack zone 3 s, all bytes whose length is n are assigned a value of c 4, which is usually used to clear struct or array data ② memcpy void * memcpy (void * dest, const void * source, size_t n); 2: copying n Bytes from source to dest 3 is not only used in heap zone, it is also used for Stack area ③ memcmp int memcmp (const void * buf1, const void * buf2, unsigned int count) memory comparison in memcmp 1, comparison results are divided into> 0, <0, = 0 "3" can be used for both heap memory and stack memory.