strcpy strcat等相关函数的实现

#include <stdio.h>
#include <assert.h>

char* MyStrcpy (char* str1, char* str2)
{
	assert (str1 != NULL && str2 != NULL);   // 断言判断 
	char* str = str1;
	while ((*str1++ = *str2++) != '\0');
	return str;
}

int MyStrlen (char* str)
{
	int n = 0;
	if (str == '\0')
		return 0;
	while (*str++ != '\0')
		n++;
	return n;
}

int MyStrcmp (char* str1, char* str2)
{
	if (str1 == NULL && str2 == NULL)
		return 0;
	int n = 0; 
	int m = 0;
	while (*str1++ != '\0')
		n++;
	while (*str2++ != '\0')
		m++;
	if (m == n)
		return 0;
	else if (n > m)
		return 1;
	else
		return -1;
}

char* MyStrcat (char str1[], char* str2)
{
	if (str1 == NULL && str2 == NULL)
		return NULL;
	if (str1 == NULL)
		return str2;
	if (str2 == NULL)
		return str1;
	char* strr = str1;
	int i = 0;
	while (1)
	{
		if (str1[i] == '\0')
			str1[i] = *str2++;
		if (*str2 == '\0')
			break;
		i++;
	}
	return strr;
}

int main (void)
{
	char str1[10] = "abc";
//	char str1[] = "abc";
	char* str2 = "defg";
	char* str = MyStrcpy (str1, str2);
	printf ("%s\n", str);
	
	int len = MyStrlen (str1);
	printf ("%d %d\n", len, sizeof(str2));
	
	int n = MyStrcmp (str1, str2);
	printf ("%d\n", n);
	
	int strr = MyStrcat (str1, str2);
	printf ("%s\n", strr);
	return 0;
}