Function Learning in C string. h.

 

 

1. memchr function, character locating. Locate character in block of memory

// 1. memchr function, character locating. Locate character in block of memory
// Void * memchr (const void *, Int, size_t );
Char * PCH;
Char STR [] = "example string ";
PCH = (char *) memchr (STR, 'P', strlen (STR); // return pointer
If (PCH! = NULL) {// cannot be found, return null
Cout <PCH <Endl; // output: ple string
Cout <"'P' at location:" <PCH-str + 1; // output: 'P' at location: 5
// After the pointer addition and subtraction operation, the output is a number (subscript)
}

2. The memcmp function compares the memory occupied by two strings.

Int memcmp (const void * ptr1, const void * ptr2, size_t num); num indicates the number of bytes to be compared.

 

Char str1 [256];
Char str2 [256];
Int N;
Gets (str1); // Gao
Gets (str2); // Tong
N = memcmp (str1, str2, 256); // 256 indicates the number of bytes for comparison. One character occupies one byte.
Cout <n <Endl; // output:-1
Return 0;

Iii. memcpy function: copy the specified number of bytes and return the copied destination address.

void * memcpy ( void * destination, const void * source, size_t num );

Char str1 [] = "sample string ";
Char str2 [40];
Char str3 [40];
Memcpy (str2, str1, strlen (str1) + 1); // strlen (str1) + 1 because the string is followed by '\ 0'
Memcpy (str3, "copy successful", 16 );
Printf ("str1: % s \ nstr2: % s \ nstr3: % s \ n", str1, str2, str3 );

// Output:
// Str1: Sample string
// Str2: Sample string
// Str3: copy successful

4. memmove function move block of memory

// Memmove function move block of memory
Char STR [] = "Gao love Tong ";
Char * P;
P = (char *) memmove (STR + 9, STR + 4 );//
Cout <STR <Endl <P;

// Output:
// Gao love
// Love

V. memset function fill block of memory

void * memset ( void * ptr, int value, size_t num );

Char STR [] = "almost every programmer shocould know memset! ";
Memset (STR, '-', 6); // '-' is directly converted to digital storage, with 6 representing the number of bytes.
Cout <STR; // output: ------ Every programmer shocould know memset!

6. strcat function, connecting two strings

char * strcat ( char * destination, const char * source );  

7. strchr: Search for characters. Locate first occurrence of character in string

const char * strchr ( const char * str, int character );      char * strchr (       char * str, int character );

Char STR [] = "This is a sample string ";
Char * PCH;
PCH = strchr (STR,'s ');
While (PCH! = NULL ){
Cout <"found at:" <PCH-str + 1 <ENL; // output the character subscript found
PCH = strchr (PCH + 1,'s ');//
}

Found at: 4
Found at: 7
Found at: 11
Found at: 18

VIII. strcmp function, string comparison

int strcmp ( const char * str1, const char * str2 );

    char * c1;
char * c2;
    c1 = "abd";
    c2 = "abcde";
    cout<<strcmp(c1,c2);

Output: 1

9. strcoll functions are similar to strcmp functions.

10. strcpy function string copying
11. strstr function, search for substrings

12. strpbrk matches all characters in string 2

 char * strpbrk (       char * str1, const char * str2 );

char str[] = "This is a sample string";
char key[] = "aeiou";
char * pch;
  printf ("Vowels in '%s': ",str);
  pch = strpbrk (str, key);
while (pch != NULL)
  {
    printf ("%c " , *pch);
    pch = strpbrk (pch+1,key);
  }
  printf ("\n");

output:

Vowels in 'This is a sample string': i i a a e i

13. Search for the final characters in strrchr. Opposite to strchr