How to return position of a substring in c?

Question

How to return position of a substring in c?

Answer 1

use strstr() which returns a pointer to the start of the leftmost occurrence of the second string in the first one. Then if strstr() returns a non-null result, use pointer arithmetic to calculate the character index:



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#include



main() {

char *s1 = "red blue green";

char *s2 = "blue";



char *s3 = strstr( s1, s2 );



if (s3) printf("String starts at position %ld\n", s3 - s1);

else printf("String not found");

}

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This prints "4" because "blue" starts at s1[4].

Answer 2

Substring In C

Answer 3

There are numerous functions available in C to achieve the purpose of finding different positions of a substring with a string.



strstr():





To obtain the first occurrence of substring in a string the function used is strstr().



The syntax for this function is



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



The header file that must be included while using this function strstr() is



In the above the function strstr() returns a pointer to the first occurrence of str2 in str1. If no match is found then NULL is returned.



strrstr():



This function is used to obtain the last occurrence of substring in a string.



The syntax for this function is



strrstr(const char *s, const char *subs );



The header file that must be included while using the function strrstr() is



This returns a pointer which points to the last occurrence of a substring within another string. If the substring is not found, this will be the NULL pointer.