C语言字符串函数操作(strlen,strcpy,strcat,strcmp)详解

int my_strlen(const char* str)
{
	int count = 0;//定义count用来记录字符串数组中字符数
	while (*str)
	{
		count++;
		str++;
	}
	return count;
}

int my_strlen1(const char* str)//以递归的方式完成字符串长度函数的模拟
{
	if (*str == '\0')
		return 0;
	return 1 + my_strlen1(str + 1);
}

int my_strlen2(char* s)//以此方式进行模拟时不能使用静态const
{
	char* p = s;
	while (*p != '\0')
		p++;
	return p - s;
}

int main()
{
	char s[10] = { 'a','b','c','d','e','f' };
	char s1[10] = { 'c','c','b' };
	printf("%s", my_strcpy(s, s1));//将s1中的字符复制到s空间中
	return 0;
}
char* my_strcpy(char* dest, const char* src)
{
	char* ret = dest;
	assert(dest != NULL);//断言
	assert(src != NULL);//断言
	while ((*dest++ = *src++));
	return ret;
}

char* my_strcat(char* dest, const char* src)
{
	char* ret = dest;
	assert(dest != NULL);
	assert(src != NULL);
	while (*dest)//访问到dest所指向字符串的最后一个字符位置
	{
		dest++;
	}
	while ((*dest++ = *src++));//将src指向的字符串复制到dest所指向字符串的后面
	return ret;
}

int my_strcmp(const char* dest, const char* src)
{
	int ret = 0;
	assert(src != NULL);
	assert(dest != NULL);
	while (!(ret = *(unsigned char*)src - *(unsigned char*)dest) && *dest)
	{
		++src;
		++dest;
	}
	if (ret < 0)
		ret = -1;
	else if (ret > 0)
		ret = 1;
	return ret;
}