1. Preface

Because the school final exam , It took 11 days to write this blog , The last blog introduced a part of string related functions and their implementation , This chapter introduces the remaining string functions and memory functions

2. String function

2.1strtok

strtok Is a function of string segmentation , Through the set segmentation assignment, a string is divided into different strings .

Its usage rules are shown in the above figure , It looks awkward and cumbersome , Next, I will use examples to demonstrate directly ：

#include<stdio.h>
#include<string.h>
int main()
{
    
	char str[] = "[email protected]@qq.com.com";
	const char *sep = "@.";
	char str1[30];
	// because strtok Will change the string being manipulated , So I make a temporary copy 
	strcpy(str1, str);
	//1.kkk
	char* ch = strtok(str1, sep);
	printf("%s\n", ch);
	//2.kkkkk
	ch = strtok(NULL, sep);
	printf("%s\n", ch);
	//3.qq
	ch = strtok(NULL, sep);
	printf("%s\n", ch);
	//4.com
	ch = strtok(NULL, sep);
	printf("%s\n", ch);
	//5.com
	ch = strtok(NULL, sep);
	printf("%s\n", ch);
}

The debugging results are as follows ：

The debugging results are shown in the figure , Every time a tag is found, it will be replaced by ‘\0’, And save the mark location , For the next time, the parameter is NULL Find other delimiters when .

improvement ：

#include<stdio.h>
#include<string.h>
int main()
{
    
	char str[] = "[email protected]@qq.com.com";
	const char *sep = "@.";
	char str1[30];
	// because strtok Will change the string being manipulated , So I make a temporary copy 
	strcpy(str1, str);
	char* ch = NULL;
	for (
	        ch = strtok(str1, sep); 
	        ch != NULL; 
	        ch = strtok(NULL, sep)
	    )
	{
    
		printf("%s\n", ch);
	}
}

2.2strerror

Is a return error code , A function that reports error information in a program .

#include<stdio.h>
#include<string.h>
#include<errno.h>
int main()
{
    
	FILE* pf;
	pf = fopen("test.txt", "r");
	printf("%s", strerror(errno));
	//errno Need a lead file #include<errno.h>
	return 0;
}

The result is as follows. , You can use it ！

3. Memory manipulation function

3.1memcmp

int main()
{
    
	int arr1[] = {
     1,2,3,4,5,7,7,7,10 };
	int arr2[] = {
     1,2,3,4,8,9,10,11,12 };
	printf(" Integer array comparison ：\n");
	printf("%d\n", memcmp(arr1, arr2, 16));
	printf("%d\n", memcmp(arr1, arr2, 28));

	printf(" String comparison ：\n");
	char str1[] = "abcdefgh";
	char str2[] = "abcdxxxx";
	printf("%d\n", memcmp(str1, str2, 4));
	printf("%d\n", memcmp(str1, str2, 6));
	return 0;
}

3.2memcpy

memcpy Is a byte copy function , Same as strcpy Use consistent , The meaning of parameter is related to *memcmp It's about the same , I won't repeat it here , Next, directly implement memcpy function

void* my_memcpy(void* dest, const void* src, size_t num)
{
    
	void* ret = dest;
	while (num--)
	{
    
		*(char*)dest = *(char*)src;
		dest = (char*)dest + 1;
		src = (char*)src + 1;
	}
	return ret;
}

int  main()
{
    
	char str1[30] = {
     0 };
	char str2[] = "abcdefg";
	my_memcpy(str1, str2, 6);
	printf("%s\n", str1);

	int arr1[] = {
     1,2,3,4,5,6,7,8,9,10 };
	int arr2[] = {
     8,8,8,8,8,8,8,8,8,8 };
	my_memcpy(arr1, arr2, 40);
	for (int i = 0; i < 10; i++)
	{
    
		printf("%d ", arr1[i]);
	}
	return 0;
}

What if we call the function like this ？

int  main()
{
    
	int arr1[] = {
     1,2,3,4,5,6,7,8,9,10 };
	my_memcpy(arr1+2, arr1, 20);
	for (int i = 0; i < 10; i++)
	{
    
		printf("%d ", arr1[i]);
	}
	return 0;
}

3.3memmove

memmove It is a library function used to deal with the problem of address overlap during assignment , Also with strcpy Have the same meaning , Used to copy data , However, it deals with data replication when space overlaps ; The specific test will not be demonstrated here , You can refer to memcpy Address overlaps for test cases ！

void* my_memmove(void* dest, const void* src, size_t num)
{
    
	void* ret = dest;
	// front -> after 
	if (dest < src)
	{
    
		while (num--)
		{
    
			*(char*)dest = *(char*)src;
			dest = (char*)dest + 1;
			src = (char*)src + 1;
		}
	}
	// after -> front 
	else
	{
    
		while (num--)
		{
    
			*((char*)dest + num) = *((char*)src + num);
		}
	}
	return ret;
}
int main()
{
    
	int arr[] = {
     1,2,3,4,5,6,7,8,9,10 };
	my_memmove(arr + 2, arr, 20);
	for (int i = 0; i < 10; i++)
	{
    
		printf("%d ", arr[i]);
	}
	printf("\n");
	char str[] = "abcdefxxxxx";
	my_memmove(str, str + 6, 5);
	printf(str);
	return 0;
}

3.4memset

memset It's an initialization function ;value Is the initial value ,num Yes bytes , This function actually initializes and assigns values to each byte .

int main()
{
    
	char str1[10];
	int arr1[10];
	memset(str1, 0, 10);
	memset(arr1, 0, 40);
	return 0;
}

Ending

This blog is over here , That is, the string related functions are roughly listed , be it so ‍*️‍*️