仿写C语言字符串处理函数

仿写标准库中的strlen、strcat、strcpy、strcmp函数，为了和标准库中的函数进行区分，自己编写的函数前添加m

仿写strlen函数

#include 

size_t mstelen(const char *str){
	if(str == NULL){
		return 0;
	}
	size_t ret = 0;
	while(*str != ''){
		str++;
		ret++;
	}
	return ret;
}

仿写strcat函数

#include 

char * mstrcat(char *destination, const char *source){
	if(destination == NULL){
		return NULL;
	}
	if(source == NULL){
		return destination;
	}
	char *ret = destination;
	while(*destination != ''){
		destination++;
	}
	while(*source != ''){
		*destination = *source;
		destination++;
		source++;
	}
	*destination = '';
	return ret;
}

仿写strcpy

#include 

char * mstrcat(char *destination, const char *source){
	if(destination == NULL){
		return NULL;
	}
	if(source == NULL){
		return destination;
	}
	char *ret = destination;
	while(*source != ''){
		*destination = *source;
		destination++;
		source++;
	}
	*destination = '';
	return ret;
}

仿写strcmp函数

#include 

int mstrcmp(const char *str1, const char *str2){
	if(str1 == NULL && str2 == NULL){
		return 0;
	}
	if(str1 == NULL && str2 != NULL){
		return 1;
	}
	if(str1 != NULL && str2 == NULL){
		return -1;
	}
	int ret = 0;
	while(1):{
		if(*str1 != *str2){
			if(*str1 > *str2){
				ret = 1;
			}else{
				ret = -1;
			}
			break;
		}
		else
		{
			if(*str1 == '' && *str2 == ''){
				break;
			}
			str1++;
			str2++;		
		}
	}
	return ret; 
}