C语言库函数

//--------------------------------------
size_t strlen( const char *string );
//--------------------------------------
//返回值用 int / size_t 各有好处
int MyStrlen(const char* str)
{
	assert(str);
	int cnt = 0;
	while (*str != '\0')
	{
		str++;
		cnt++;
	}
	return cnt;
}
int main()
{
	char arr[] = "bacon";
	printf("%d\n", MyStrlen(arr));
	return 0;
}

//-------------------------------------
char* strcpy(char* dest, const char* src)
//-------------------------------------
char* MyStrcpy(char* dest, const char* src)
{
	assert(dest && src);
	char* ret = dest;
	while (*dest++ = *src++);
	return ret;
}
int main()
{
	char str1[30] = "Bacon";
	char str2[] = " is your friend.";
	MyStrcpy(str1 + 5, str2);
	printf("%s\n", str1);
	return 0;
}
//Bacon is your friend.
//------------------------------------------------------------
char* strcpy(char* dest, const char* src, size_t num)
//---------------------------------------------------------------
char* MyStrncpy(char* dest, const char* src, size_t num)
{
	assert(dest && src);
	char* ret = dest;
	while (num--)
	{
		*dest++ = *src++;
	}
	return ret;
}
int main()
{
	char str1[20] = { 0 };
	char str2[] = "bacon";
	printf("%s\n", MyStrncpy(str1, str2, 4));
	return 0;
}
//baco

//-----------------------------------------------
int strcmp(const char* str1, const char* str2)
//-----------------------------------------------
int MyStrcmp(const char* str1, const char* str2)
{
	assert(str1 && str2);
	while (*str1 != '\0' && *str2 != '\0' && *str1 == *str2)
	{
		str1++;
		str2++;
	}
	if (*str1 == *str2)
		return 0;
	else if (*str1 > *str2)
		return 1;
	else
		return -1;
}
int main()
{
	char str1[] = "abcdef";
	char str2[] = "abcdfe";
	printf("%d\n", MyStrcmp(str1, str2));
	return 0;
}
//-1
//-----------------------------------------------------
int strncmp(const char* str1, const char* str2, size_t num)
//---------------------------------------------------------
int MyStrncmp(const char* str1, const char* str1, size_t num)
{
	assert(dest && src);
	while (num--)
	{
		if (*str1!= *str2)
		{
			if (*str1> *str2)
				return 1;
			else
				return -1;
		}
		str1++;
		str2++;
	}
	return 0;
}
int main()
{
	char str1[] = "abcdef";
	char str2[] = "abcdfe";
	printf("%d\n", MyStrncmp(str1, str2, 5));
	return 0;
}

//----------------------------------------------
char* strcat(char* dest, const chat* src)
//----------------------------------------------
char* MyStrcat(char* dest, const char* src)
{
	assert(dest && src);
	char* ret = dest;
	//找到字符串结尾
	while (*dest != '\0')
	{
		dest++;
	}
	while (*dest++ = *src++);
	return ret;
}
int main()
{
	char str1[20] = "bacon";
	char str2[] = " king";
	printf("%s\n", MyStrcat(str1 , str2));
	return 0;
}
//bacon king
//----------------------------------------------------------
char* strncat(char* dest, const char* src, size_t num);
//----------------------------------------------------------
char* MyStrncat(char* dest, const char* src, size_t num)
{
	assert(dest && src);
	char* ret = dest;
	while(*dest != '\0')
	{
		dest++;
	}
	while (num--)
	{
		*dest++ = *src++;
	}
	return ret;
}
int main()
{
	char str1[30] = "Bacon";
	char str2[] = " is your friend";
	printf("%s\n", MyStrncat(str1, str2, 8));
	return 0;
}
//Bacon is your

//------------------------------------------------
char* strstr(const char* str1, const char* str2)
//--------------------------------------------------
char* MyStrstr(const char* str1, const char* str2)
{
	assert(str1 && str2);
	char* p = str1;
	char* s1 = str1;
	char* s2 = str2;
	while (*p)//str1走完就可以跳出了
	{
		//找到可能匹配的位置
		while (*s1 != *s2)
		{
			s1++;
		}
		p = s1;
		while (*s1 != '\0' && *s2 != '\0' && *s1 == *s2)
		{
			s1++;
			s2++;
		}
		if (*s2 == '\0')
		{
			return p;
		}
		else
		{
			s1 = p + 1;
			s2 = str2;
			p = s1;
		}
	}
	return NULL;
}
int main()
{
	char str1[] = "abbbcdef";
	char str2[] = "bbc";
	printf("%s\n", MyStrstr(str1, str2));
	return 0;
}

//---------------------------------------------
char* strtok(char* str , const char* sep)
//---------------------------------------------
//由函数定义：我们需要多次切分的时候——第一次传字符串地址，之后传NULL
int main()
{
	char* p = "SiDiuPiDe233@icloud.com";
	char sep[] = "@.";
	char arr[30];
	strcpy(arr, p);
	char* i = NULL;
	for (i = strtok(arr, sep); i != NULL; i = strtok(NULL, sep))
	{
		printf("%s\n", i);
	}
	return 0;
}

//---------------------------------
char* strerror(int errnum);
//-----------------------------------
int main()
{
	FILE* p = fopen("test.txt", "r");
	if (NULL == p)
		printf("%s\n", strerror(errno));
	return 0;
}