Is there a C library function that will return the index of a character in a string?
So far, all I've found are functions like strstr that will return the found char *, not it's location in the original string.
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7 Answers
strstr returns a pointer to the found character, so you could use pointer arithmetic: (Note: this code not tested for its ability to compile, it's one step away from pseudocode.)
char * source = "test string"; /* assume source address is */
/* 0x10 for example */
char * found = strstr( source, "in" ); /* should return 0x18 */
if (found != NULL) /* strstr returns NULL if item not found */
{
int index = found - source; /* index is 8 */
/* source[8] gets you "i" */
}
4 Comments
R.. GitHub STOP HELPING ICE
Undefined behavior if the character is not found. Also you should not use
strstr (with or without the typo) if strchr would suffice.
Bill
@R.. - I fixed the typo and added error checking to the pseudocode. Also,
strchr does not work for finding multi-character sequences, does it?R.. GitHub STOP HELPING ICE
Indeed, but OP asked for a character not a substring. Of course if you interpret character broadly to include multibyte characters,
strstr is the right function to use.Bill
@R.. - Since the OP was talking about a character as in text, not as in the
char storage name, I gave a solution that has a hope of working for a character like 輪. You object?I think that
size_t strcspn ( const char * str1, const char * str2 );
is what you want. Here is an example pulled from here:
/* strcspn example */
#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;
}
4 Comments
Isak Savo
strcspn is more like String.IndexOfAny() - searching for any of the characters in the keys array. But yeah, it'll do the trick
GreenieMeanie
The above comment is very important - doing it as in the example DOES NOT mimic indexOf(), so the original answer is pretty much incorrect.
Alessandro Muzzi
This is exactily what you are looking for: stackoverflow.com/a/1479401/3395760
EDIT: strchr is better only for one char. Pointer aritmetics says "Hellow!":
char *pos = strchr (myString, '#');
int pos = pos ? pos - myString : -1;
Important: strchr () returns NULL if no string is found
1 Comment
Ed Graham
You might want to rewrite the second line as
int ipos = pos ? pos - myString : -1; to avoid compiler errors - but otherwise this still works in 2023!You can use strstr to accomplish what you want. Example:
char *a = "Hello World!";
char *b = strstr(a, "World");
int position = b - a;
printf("the offset is %i\n", position);
This produces the result:
the offset is 6
1 Comment
R.. GitHub STOP HELPING ICE
UB if there is no match (subtraction of pointers not within the same object).
Write your own :)
Code from a BSD licensed string processing library for C, called zString
https://github.com/fnoyanisi/zString
int zstring_search_chr(char *token,char s){
if (!token || s=='\0')
return 0;
for (;*token; token++)
if (*token == s)
return 1;
return 0;
}
Comments
If you are not totally tied to pure C and can use string.h there is strchr() See here
1 Comment
Robert Gamble
I'm not sure what you mean by "pure C" but strchr() and string.h have been part of Standard C for 20 years.
You can write
s="bvbrburbhlkvp";
int index=strstr(&s,"h")-&s;
to find the index of 'h' in the given garble.
