C语言 字符串-字符串的复制

字符串复制函数：

strcpy(目标字符串的首地址,被复制的字符串的首地址)

  复制p到a：

	char * p="12345";
	char a[20];
	strcpy(a, p);
	printf("%s\n", a);

 strcpy_s(目标字符串的首地址,缓冲长度,被复制的字符串的首地址)

	strcpy_s(a, 20, p);//20为缓冲长度 可用空间的长度
	printf("%s\n", a);

strncpy(目标字符串的首地址,被复制的字符串的首地址,复制的长度) ，这种复制方式更像是覆盖

	strncpy(a, "123456", 4);

strncpy_s(目标字符串的首地址,缓冲长度,被复制的字符串的首地址,,复制的长度)，清零后复制

	strncpy_s(a, 20, "123456", 4);

仿真字符串复制函数 strcpy

char* my_strcpy(char* dest, const char* src);

char* my_strcpy(char* dest, const char* src)
{
	char* p_dest = dest;
	const char* p_src = src;
	while (*p_src)//!='\0'
	{
		*p_dest = *p_src;
		p_src++;
		p_dest++;
	}
	*p_dest = '\0';
	return dest;
}

测试：

printf("%s\n", my_strcpy(a, "how are you"));

仿真字符串复制函数 strncpy

char* my_strncpy(char* dest, const char* src, unsigned num);

char* my_strncpy(char* dest, const char* src, unsigned num)
{
	char* p_dest = dest;
	const char* p_src = src;
	int i = 0;
	while (*p_src && i++ < num)//!='\0'
	{
		*p_dest = *p_src;
		p_src++;
		p_dest++;
	}
	//*p_dest = '\0';
	return dest;
}

测试：

  my_strncpy(a, "123456", 4);

完整代码：

#include 
#include 
char* my_strcpy(char* dest, const char* src);
char* my_strncpy(char* dest, const char* src, unsigned num);
int main ()
{
	/*字符串复制函数*/ 
	char * p="12345";
	char a[20];
	/*strcpy*/
	//a=p;
	strcpy(a, p);
	printf("%s\n", a);
	printf("%s\n", my_strcpy(a, "how are you"));
	printf("%d\n", strlen(strcpy(a, "how old are you")));
	/*strcpy_s*/
	strcpy_s(a, 20, p);//20为缓冲长度 可用空间的长度
	printf("%s\n", a);

	/*strncpy*/

	my_strncpy(a, "123456", 4);//像是覆盖
	strncpy(a, "123456", 4);//像是覆盖

	printf("%s\n", a);

	/*strncpy_s*/
	strncpy_s(a, 20, "123456", 4);//清零后复制
	printf("%s\n", a);
	/*仿真字符串复制函数 strcpy   */
	return 0;
}

char* my_strcpy(char* dest, const char* src)
{
	char* p_dest = dest;
	const char* p_src = src;
	while (*p_src)//!='\0'
	{
		*p_dest = *p_src;
		p_src++;
		p_dest++;
	}
	*p_dest = '\0';
	return dest;
}

char* my_strncpy(char* dest, const char* src, unsigned num)
{
	char* p_dest = dest;
	const char* p_src = src;
	int i = 0;
	while (*p_src && i++ < num)//!='\0'
	{
		*p_dest = *p_src;
		p_src++;
		p_dest++;
	}
	//*p_dest = '\0';
	return dest;
}

完整输出：