Pzk learns string function of C language (1)

One 、 String function ：

1. String comparison function strcmp

The function prototype ：int strcmp(const char *s1, const char *s2);
do use ： Compare s1 and s2 Is the string the same
ginseng Count ：s1 Is the first string to compare
s2 Is the second string to compare
return return ： 0 If two strings are the same
<0 The first string is less than the second string
>0 The first string is larger than the second string
The comparison is the first different character ascii The difference between the values of .

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#include <stdio.h>
#include <string.h>
#include <strings.h>
int main()
{
    
	char str1[20];// Define string 
	char str2[20];
	int temp;
	
	printf(" Please enter two strings \n");
	gets(str1);// Get the input string from the keyboard 
	gets(str2);

	temp = strcmp(str1,str2);// obtain strcmp The return value of  
	printf("%d",temp);
	return 0;
}

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2. Get the string length strlen

The function prototype ： size_t strlen(const char *s);
effect ： Get the effective length of the string
Parameters ： You need to get the string content of length
return ： s The effective length of the string

#include <stdio.h>
#include <string.h>
#include <strings.h>
int main()
{
    
	char str1[20];// Define string 
	int temp;
	
	printf(" Please enter the string \n");
	gets(str1);// Get input 

	temp = strlen(str1);//strlen The return value of is the effective length of the return string , barring \0; 
	printf("%d",temp);
	return 0;
}

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3. String append strcat

The function prototype ：char *strcat(char *dest, const char *src);
effect ： hold src String concatenation to dest After the string
Parameters ： src The source string , It needs to be spliced to dest String after
dest Destination string , Need to store src character string .
return ： Return the string content after splicing .

#include <stdio.h>
#include <string.h>
#include <strings.h>
int main()
{
    
	char str1[20];
	char str2[20];
	memset(str1,1,sizeof(str1));// Initialize string , You don't have to write , It's better to write ;
	printf("arr[0] = %d\n",str1[0]);
	printf(" Please enter two strings \n");
	gets(str1);
	gets(str2);

	if(strncmp(str1,str2,5) == 0)// Compare str1 and str2 The first five characters of 
	{
    
		strncat(str1,str2,3);// Additional , hold str2 The first three characters of are appended to str1 in 
	}
	puts(str1);
	return 0;
}

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4. String splicing sprintf

The function prototype ：int printf(const char *format, …);
effect ： Combine the contents of variable length parameters into a string format
Parameters ： The first part ： String variable ,
Second part ： The contents of double quotes , There are placeholders
The third part ： Various variables , Used to fill the placeholder .
return ： String length after splicing ..

#include <stdio.h>
#include <string.h>

int main(int argc ,char* argv[])
{
    
	char arr1[20] = "abcdf";
	char arr2[] = "abcdf";

	printf("arr1 = %s\n",arr1);
	int a = 10;
	int b = 20;
    
    int temp;
	temp=sprintf(arr1,"daniubi-%d-%d",a,b);
    // hold a and b Put variables in placeholders , Then assign the whole string to arr1, Will overwrite arr1 The original content ;
	printf("arr1=%s\n temp =%d\n",arr1,temp);
    system("pause");
	return 0;
}

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5. Input of string

        char *gets(char *s);
         effect ： Get a string , End with enter .
         Parameters ： Where to save the entered content .
         Return value ： The contents of the input string .
         Be careful ： Can't detect s Of memory space , Avoid using .

#include <stdio.h>
#include <string.h>
int main()
{
    
	printf(" Enter a string \n");
	char str[20]= {
    0};
	gets(str);// Enter a string from the keyboard 
	
	printf("str = %s\n",str);
	return 0;
}

int getchar(void);
effect ： Get an input character
Parameters ： No parameter
Return value ： Of the characters entered ascii value .

Be careful ： The input function is a blocking function , If there is no input, wait until the input ends .

#include <stdio.h>
#include <string.h>
int main()
{
    
	printf(" Enter a character \n");
	getchar();// Get a character from the keyboard 
	
	int temp = getchar();
	printf("temp = %d",temp);
	return 0;
}

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6. String output

       int putchar(int c);
        effect ： Output a character 
        Parameters ： Characters to be output ascii value 
        return ： Also output ascii value 

int puts(const char *s);
effect ： Output a string
Parameters ： The string content that needs to be output
Return value ： The number of characters of the output string , contain \0

#include <stdio.h>
#include <string.h>
int main()
{
    
	printf(" Enter a string \n");
	char str[20]= {
    0};
	gets(str);
	
	puts(str);
	return 0;
}

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7. Copy of string

      char *strcpy(char *dest, const char *src);
       effect ： Copy src Content to dest in 
       Parameters ： src The source string 
                 dest  Destination string 
        Return value ： The copied string   dest character string .

char *strncpy(char *dest, const char *src, size_t n);
effect ： Copy src In front of n Characters .
Parameters ： src The source string
dest Destination string
n The number of strings to be copied
Return value ： The copied string dest character string .