[C language] some commonly used string functions -- learning notes

1、strcat(buf, text);

effect ： Used to connect two strings
Use cases , Connect buf+text：

#include <stdio.h>
#include <string.h>
 
int main ()
{
    
   char src[50], dest[50];
 
   strcpy(src,  "This is source");
   strcpy(dest, "This is destination");
 
   strcat(dest, src);
 
   printf(" The final target string ： |%s|", dest);
   
   return(0);
}

2、strcpy()

strcpy() The function is C A library function in the language that copies strings
Use cases , take c Copied to the a：

#include<string.h>
#include <stdio.h>
void main()
{
    
	char a[20], c[] = "I am a teacher!";
	strcpy(a, c);
	printf(" c=%s\n", c);
	printf(" a=%s\n", a);

}

3、sprintf()

sprintf() Function is to print content into buffer[]
Use cases ：

#include<string.h>
#include <stdio.h>
int main()
{
    
    int ddd=666;
    char *buffer=NULL;    
    if((buffer = (char *)malloc(80*sizeof(char)))==NULL)
    {
    
        printf("malloc error\n");
    }
    sprintf(buffer, "The value of ddd = %d", ddd);//The value of ddd = 666
    printf("%s\n",buffer);
    free(buffer);
    buffer=NULL;
    return 0;
}

4、strstr()

Look for the first time “IPD” The location of the sign ,
such as ：strstr(buff, “IPD,”); // stay buf Mid search “IPD” head

#include <stdio.h>
#include <string.h>
int main()
{
    
   const char buff[20] = "WWW.IPD:hello";
   const char need[10] = "IPD";
   char *ret;
 
   ret = strstr(haystack, need);
 
   printf(" The substring is ： %s\n", ret);
   
   return(0);
}

The function returns in buff For the first time need The location of the string , If not found, return null

5、strchr()

strchr() The function searches for the first occurrence of a string in another string
such as ：strchr(buff, ‘:’); // stay buff Find ’:’

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

int main ()
{
    
   const char buff[] = "IPD:liangwwff ";
   const char ch = ':';
   char *ret;

   ret = strchr(buff, ch);

   printf("|%c|  The following string is  - |%s|\n", ch, ret);
   
   return(0);
}

This function returns the string str The first occurrence of the character c The location of , If the character is not found, returns NULL.

6、strlen()

strlen() Function to find the length of a string （ How many characters are included ）

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

void main()
{
    
    char str[100] = {
     0 };
    size_t len;
    gets(str);
    len = strlen(str);
    printf("Length: %d\n", len);
}