自制函数实现strlen、strcpy、strcmp、strcat函数

C语言代码实现如下：

/*************************************************************************
    > File Name:    1.c
    > Author:       Macro Red
    > Mail:         [email protected] 
    > Environment:  Lunix Ubuntu 16.04 LTS 
    > Created Time: 2018-01-29 16:36
 ************************************************************************/

/* Standard includes. */
#include 
/* Library includes.  */
/* User files         */

int MyStrlen(char a[]);
int MyStrlen2(const char* s);
char *MyStrcpy(char a[], const char b[]);
int MyStrcmp(const char a[], const char b[]);
char *MyStrcat(char a[], const char b[]);


/**
* @brief  main function
* @param  None
* @retval None
*/
int main(void)
{
	char ch1[20] = {0}, ch2[20] = "Hello";

	printf("ch1:%s\tch2:%s\n", ch1, ch2);
	printf("MyStrlen(ch1):%d,MyStrlen(ch2):%d\n", MyStrlen(ch1), MyStrlen(ch2));
	printf("MyStrcmp(ch1,ch2):%d\n", MyStrcmp(ch1,ch2));
	printf("MyStrcat(ch1,ch2):%s\n", MyStrcat(ch1,ch2));
	printf("MyStrcpy(ch1,ch2):%s\n", MyStrcpy(ch1,ch2));
	printf("ch1:%s\tch2:%s\n", ch1, ch2);
	
	return 0;
}


/**
* @brief  user "strlen"
* @param  char a[]
* @retval int
*/
int MyStrlen(char a[])
{
	int count = 0;
	while(a[count++] != '\0');
	return count-1;
}

/**
* @brief  user "strlen2"
* @param  char a[]
* @retval int
*/
int MyStrlen2(const char* s)
{
	return (*s?(strlen(s + 1) + 1) : 0);
}


/**
* @brief  user "strcpy"
* @param  char a[], const char b[]
* @retval None
*/
char *MyStrcpy(char a[], const char b[])
{
	int i;
	for(i = 0; b[i] != '\0'; i++)
	{
		a[i] = b[i];
	}
	a[i] = '\0';
	return a;
}


/**
* @brief  user "strcmp"
* @param  const char a[], const char b[]
* @retval int
*/
int MyStrcmp(const char a[], const char b[])
{
	int i;
	for(i = 0; a[i] != '\0' && b[i] != '\0'; i++)
	{
		if(a[i] < b[i])
			return -1;
		else if(a[i] > b[i])
			return 1;
	}

	if(a[i] == '\0' && b[i] == '\0')
		return 0;
	else if(a[i] == '\0')
		return -1;
	else if(b[i] == '\0')
		return 1;

	return 0;
}

/**
* @brief  user "strcat"
* @param  char a[], const char b[]
* @retval None
*/
char *MyStrcat(char a[], const char b[])
{
	int a_falg, i;
	a_falg = MyStrlen(a);
	for(i = 0; b[i] != '\0'; i++)
	{
		a[i+a_falg] = b[i];
	}
	a[i+a_falg] = '\0';
	return a;
}