C语言标准库 常用函数说明
void *memset(void *str, int c, size_t n)
Syntax
void *memset(void *str, int c, size_t n)
Description:
The C library function void *memset(void *str, int c, size_t n) copies the character c (an unsigned char) to the first n characters of the string pointed to, by the argument str.
Parameters:
- str -- This is a pointer to the block of memory to fill.
- c -- This is the value to be set. The value is passed as an int, but the function fills the block of memory using the unsigned char conversion of this value.
- n -- This is the number of bytes to be set to the value.
Return Value:
This function returns a pointer to the memory area str.
void *memchr(const void *str, int c, size_t n)
Description
The C library function void *memchr(const void *str, int c, size_t n) searches for the first occurrence of the character c (an unsigned char) in the first n bytes of the string pointed to, by the argument str.
Parameters
-
str -- This is the pointer to the block of memory where the search is performed.
-
c -- This is the value to be passed as an int, but the function performs a byte per byte search using the unsigned char conversion of this value.
-
n -- This is the number of bytes to be analyzed.
Return Value
This function returns a pointer to the matching byte or NULL if the character does not occur in the given memory area.
从buf所指内存区域的前count个字节查找字符ch。当第一次遇到字符ch时停止查找。如果成功，返回指向字符ch的指针；否则返回NULL。
int memcmp(const void *str1, const void *str2, size_t n)
Description
The C library function int memcmp(const void *str1, const void *str2, size_t n)) compares the first n bytes of memory area str1 and memory area str2.
Parameters
-
str1 -- This is the pointer to a block of memory.
-
str2 -- This is the pointer to a block of memory.
-
n -- This is the number of bytes to be compared.
Return Value
-
if Return value < 0 then it indicates str1 is less than str2.
-
if Return value > 0 then it indicates str2 is less than str1.
-
if Return value = 0 then it indicates str1 is equal to str2.
void *memmove(void *str1, const void *str2, size_t n)
Description
The C library function void *memmove(void *str1, const void *str2, size_t n) copies n characters from str2 to str1, but for overlapping memory blocks, memmove() is a safer approach than memcpy().
Declaration
Following is the declaration for memmove() function.
Parameters
-
str1 -- This is a pointer to the destination array where the content is to be copied, type-casted to a pointer of type void*.
-
str2 -- This is a pointer to the source of data to be copied, type-casted to a pointer of type void*.
-
n -- This is the number of bytes to be copied.
Return Value
This function returns a pointer to the destination, which is str1.
