1.实现strcpy 2.实现strcat 3.实现strstr 4.实现strchr 5.实现strcmp 6.实现memcpy 7.实现memmove

妖狐艹你老母 2024-04-17 15:21 28阅读 0赞

//assert 断言，用于提示一些可能存在的错误，相较于if的作用更加的激烈。
    //strcpy:复制
    char* Strcpy(char* dest, const char* source){
    	char* ret = dest;
    	assert(dest != NULL && source != NULL);
    	while (*dest++ = *source++){
    		;
    	}
    	return ret;
    }
    
    
    //strcat:拼接
    char* Strcat(char* dest, const char* source){
    	char* ret = dest;
    	assert(dest != NULL && source != NULL);
    	while (*dest != '\0'){
    		*dest++;
    	}
    	while (*dest++ = *source++){
    		;
    	}
    	return ret;
    }
    
    //strstr:判断一个字符串里是否包含另一个。
    char* Strstr(const char* dest, const char* src){
    	const char* str1 = dest;
    	const char* str2 = src;
    	const char* ret = dest;
    	assert(dest != NULL && src != NULL);
    	if (*src == '\0'){
    		return (char*)dest;
    	}
    	while (*ret){
    		str1 = ret;
    		str2 = src;
    	}
    	while (*str1 && *str2 && *str1 == *str2){
    		str1++;
    		str2++;
    	}
    	if (*str2 == '\0'){
    		return (char*)ret;
    	}
    	return NULL;
    }
    
    //strcmp:字符串比较
    char* Strcmp(const char* dest, const char* src){
    	assert(dest != NULL && src != NULL);
    	while (*dest == *src){
    		if (*dest == '\0'){
    			return 0;
    		}
    		dest++;
    		src++;
    	}
    	return *dest - *src;
    }
    
    //memcpy :内存的拷贝，定义在string.h里。
    void* Memcpy(void* dest, void* src, int count){
    	void* ret= dest;
    	assert(dest != NULL && src != NULL);
    	while (count--){
    		*(char*)dest = *(char*)src;
    		((char*)dest)++;
    		((char*)src)++;
    	}
    	return ret;
    }
    
    //memmove：在一个内存中拷贝，可以理解为memcpy的升级版，解决缓冲区的重叠
    void* my_memmove(void* dest,void* src, size_t count){
    	void* ret = dest;
    	if (dest <= src || (char*)dest >= ((char*)src + count)) {
    		while (count--) {
    			*(char*)dest = *(char*)src;
    			dest = (char*)dest + 1;
    			src = (char*)src + 1;
    		}
    	}
    	else {
    		dest = (char*)dest + count - 1;
    		src = (char*)src + count - 1;
    		while (count--) {
    			*(char*)dest = *(char*)src;
    			dest = (char*)dest - 1;
    			src = (char*)src - 1;
    		}
    	}
    	return(ret);
    
    }
    
    
    
    //strchr:是查找字符串dest中首次出现src的位置。
    char* my_strchr(char* dest, char src){
    	while (*dest != '\0' && *dest != 'src'){
    		dest++;
    	}
    	return *dest == src ? dest : NULL;
    }