C Language Strings Find first/last occurrence of a specific character: strchr(), strrchr()
Example
The strchr and strrchr functions find a character in a string, that is in a NUL-terminated character array. strchr return a pointer to the first occurrence and strrchr to the last one.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
char toSearchFor = 'A';
/* Exit if no second argument is found. */
if (argc != 2)
{
printf("Argument missing.\n");
return EXIT_FAILURE;
}
{
char *firstOcc = strchr(argv[1], toSearchFor);
if (firstOcc != NULL)
{
printf("First position of %c in %s is %td.\n",
toSearchFor, argv[1], firstOcc-argv[1]); /* A pointer difference's result
is a signed integer and uses the length modifier 't'. */
}
else
{
printf("%c is not in %s.\n", toSearchFor, argv[1]);
}
}
{
char *lastOcc = strrchr(argv[1], toSearchFor);
if (lastOcc != NULL)
{
printf("Last position of %c in %s is %td.\n",
toSearchFor, argv[1], lastOcc-argv[1]);
}
}
return EXIT_SUCCESS;
}
Outputs (after having generate an executable named pos):
$ ./pos AAAAAAA
First position of A in AAAAAAA is 0.
Last position of A in AAAAAAA is 6.
$ ./pos BAbbbbbAccccAAAAzzz
First position of A in BAbbbbbAccccAAAAzzz is 1.
Last position of A in BAbbbbbAccccAAAAzzz is 15.
$ ./pos qwerty
A is not in qwerty.
One common use for strrchr is to extract a file name from a path. For example to extract myfile.txt from C:\Users\eak\myfile.txt:
char *getFileName(const char *path)
{
char *pend;
if ((pend = strrchr(path, '\')) != NULL)
return pend + 1;
return NULL;
}
