Memset, memcpy, and atoi Functions

1. Void * memset (void * s, int C, size_t N)

Purpose: set the value of the first n Bytes of the memory space S to the value c.

2. Example

＃includevoid main(){char *s="Golden Global View";clrscr();memset(s,‘G‘,6);printf("%s",s);getchar();return 0;}

3. The memset () function is often used for memory space initialization. For example:

char str[100];memset(str,0,100);

4. Deep connotation of memset (): it is used to set all memory space to a specific character. It is generally used to initialize the defined string to ''or '/0'. For example: char A [100]; memset (A, '/0', sizeof ());

Memcpy is used for memory copying.You can use it to copy any data type object and specify the length of the copied data. For example, char a [100], B [50]; memcpy (B,, sizeof (B); If sizeof (a) is used, the memory address of B may overflow.

Strcpy can only copy strings. It ends copying when '/0' is encountered. For example, char a [100], B [50]; strcpy (A, B ); if strcpy (B, A) is used, check whether the length of the string in A (before the first '/0') exceeds 50 bits. If it exceeds, this will cause memory address overflow of B.

5. Added: Some experiences
Memset can easily clear a variable or array of the structure type.
For example:

struct sample_struct{char csName[16];int iSeq;int iType;};

For Variables

struct sample_strcut stTest;

In general, the method of clearing sttest is as follows:

stTest.csName[0]=‘/0‘;stTest.iSeq=0;stTest.iType=0;

Memset is very convenient:

memset(&stTest,0,sizeof(struct sample_struct));

If it is an array:

struct sample_struct TEST[10];

Then

memset(TEST,0,sizeof(struct sample_struct)*10);

6. Strcpy

Prototype: extern char * strcpy (char * DEST, char * SRC );
Usage: # I nclude
Function: Copies the string ending with null indicated by Src to the array indicated by DeST.
Note: The memory areas specified by Src and DEST cannot overlap and DEST must have sufficient space to accommodate SRC strings.
Returns the pointer to DeST.
Memcpy
Prototype: extern void * memcpy (void * DEST, void * SRC, unsigned int count );
Usage: # I nclude
Function: copy count bytes from the memory area indicated by Src to the memory area indicated by DeST.
Note: the memory areas specified by Src and DEST cannot overlap. The function returns a pointer to DeST.
Memset
Prototype: extern void * memset (void * buffer, int C, int count );
Usage: # I nclude
Function: sets the first count byte of the memory area referred to by buffer to character C.
Note: The pointer to the buffer is returned.

Atoi () function

Prototype: int atoi (const char * nptr)

Usage: # include <stdlib. h>

Function: converts a string to an integer. atoi () scans the nptr parameter string and skips the leading space character until the conversion starts when a number or positive or negative sign is encountered, when a non-digit or string ('\ 0') is encountered, the conversion is terminated and the result is returned.

Description: The atoi () function returns the converted integer.

Memset, memcpy, and atoi Functions