Use of strtok and strError

One .strtok

char* strtok ( char* str, const char* sep );

sep --- sep The parameter is a string , Defines the set of characters used as separators

char arr[] = " [email protected] " ; // 2913679329 qq com

char* p = " @. " ;

strtok function ： From the address of the first character Look backwards one by one arr The separator in （@ and .） Change it to ‘\0’ And then print ; Then from the next character address of the separator Look backwards one by one arr The second separator in Change it to ‘\0’ And then print ; Execute sequentially , until   The next character address of the separator Look backwards one by one find arr Medium ‘\0’ stop .

Only one section can be cut at a time , The starting address of the first incoming string , Pass in null pointer for the second time

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<string.h>


int main()
{
	char arr[] = "[email protected]";
	const char* p = "@.";

	char buf[1024] = { 0 };
	strcpy(buf, arr);

	char* ret = NULL;

	for (ret = strtok(arr, p); ret != NULL; ret = strtok(NULL, p))
	{
		printf("%s\n", ret);
	}
	
	return 0;
}

  Be careful ：

1.strtok Function changes the string being manipulated , Therefore, when used, the segmented string is generally a temporary copy of the content and can be modified

2.strtok The first argument of the function is not NULL, Function will find str The first mark in ,strtok The function will save its position in the string

3.strtok The first argument to the function is NULL, The function will start at the same position in the string that is saved （ Start at position after marking ）, Find next tag

4. If there are no more tags in the string , Then return to NULL. 

Two .strerror

strerror --- Return error code , The corresponding error message

char* strerror ( int errnum );

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>

int main()
{
	//error Is a global error code variable 
	// When C Language library functions in the process of execution , Something went wrong , The corresponding error code , Assign values to the errno in 

	FILE* pf = fopen("test.txt", "r");

	if (pf == NULL)
	{
		printf("%s\n", strerror(errno));
	}
	else
	{
		printf("open file success\n");
	}
	return 0;
}