<string.h> header functions (4) - Search

Search Functions

strchr : Locate first occurrence of character in string

const char* strchr(const char* str, int character); //for C++
      char* strchr(      char* str, int character); //for C

str : C string

character : Character to be located. It is passed as its int promotion, but it is internally converted back to char for the comparison.

Return Value

A pointer to the first occurrence of character in str. If the character is not found, the function returns a null pointer.

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

int main ()
{
  char str[] = "This is a sample string";
  char * pch;
  printf ("Looking for the 's' character in \"%s\"...\n",str);
  pch=strchr(str,'s');
  while (pch!=NULL)
  {
    printf ("found at %d\n",pch-str+1);
    pch=strchr(pch+1,'s');
  }
  return 0;
}

Looking for the 's' character in "This is a sample string"...
found at 4
found at 7
found at 11
found at 18

---

strcspn : Get span until character in string

size_t strcspn(const char* str1, const char* str2);

str1 : C string to be scanned.

str2 : C string containing the charcters to match.

Return Value

The length of the initial part of str1 not containing any of the characters that are part of str2.

This is the length of str1 if none of the characters in str2 are found in str1.

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

int main ()
{
  char str[] = "fcba73";
  char keys[] = "1234567890";
  int i;
  i = strcspn (str,keys);
  printf ("The first number in str is at position %d.\n",i+1);
  return 0;
}

The first number in str is at position 5

---

strpbrk : Locate characters in string

const char* strpbrk(const char* str1, const char* str2); //for C++
      char* strpbrk(      char* str1, const char* str2); //for C

str1 : C string to be scanned.

str2 : C string containing the characters to match.

Return Value

A pointer to the first occurrence in str1 of any of characters that are part of str2, or a null pointer if none of the characters of str2 is found in str1 before the terminating null-character.

If none of the characters of str2 is found in str1, a null pointer is returned.

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

int main ()
{
  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");
  return 0;
}

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

---

strrchr : Locate last occurrence of character in string

const char* strrchr(const char* str, int character); //for C++
      char* strrchr(      char* str, int character); //for C

str : C string

character : Character to be located. It is passed as its int promotion, but it is internally converted back to char.

Return Value

A pointer to the last occurrence of character in str.

If the character is not found, the function returns a null pointer.

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

int main ()
{
  char str[] = "This is a sample string";
  char * pch;
  pch=strrchr(str,'s');
  printf ("Last occurence of 's' found at %d \n",pch-str+1);
  return 0;
}

Last occurrence of 's' found at 18

---

strspn : Get span of character set in string

size_t strspn(const char* str1, const char* str2);

str1 : C string to be scanned

str2 : C string containing the characters to match

Return Value

The length of the initial portion of str1 containing only characters that appear in str2.

Therefore, if all of the charactres in str1 are in str2, the function returns the length of the entire str1 string, and if the first character in str1 is not in str2, the function returns zero.

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

int main ()
{
  int i;
  char strtext[] = "129th";
  char cset[] = "1234567890";

  i = strspn (strtext,cset);
  printf ("The initial number has %d digits.\n",i);
  return 0;
}

The initial number has 3 digits.

---

strstr : Locate substring

const char* strstr(const char* str1, const char* str2); //for C++
      char* strstr(      char* str1, const char* str2); //for C

str1 : C string to be scanned.

str2 : C string containing the sequence of characters to match.

Return Value

A pointer to the first occurence in str1 of the entire sequence of characters specified in str2, or a null pointer if the sequence is not present in str1.

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

int main ()
{
  char str[] ="This is a simple string";
  char * pch;
  pch = strstr (str,"simple");
  strncpy (pch,"sample",6);
  puts (str);
  return 0;
}

This is a sample string

---

strtok : Split string into tokens

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

str : C string to truncate.

delimiters : C string containing the delimiter characters.

Return Value

If a token is found, a pointer to the beginning of the token. Otherwise, a null pointer.

A null pointer is always returned when the end of the string is reached in the string being scanned.

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

int main ()
{
  char str[] ="- This, a sample string.";
  char * pch;
  printf ("Splitting string \"%s\" into tokens:\n",str);
  pch = strtok (str," ,.-");
  while (pch != NULL)
  {
    printf ("%s\n",pch);
    pch = strtok (NULL, " ,.-");
  }
  return 0;
}

Splitting string "- This, a sample string." into tokens:
This
a
sample
string