I am doing something in C which requires use of the strings (as most programs do).
Looking in the manpages, I found, at string(3):
SYNOPSIS
#include <strings.h> char * index(const char *s, int c) (...) #include <string.h> char * strchr(const char *s, int c)
So I curiously looked at both strchr(3) and index(3)...
And I found that both do the following:
The strchr()/index() function locates the first occurrence of c in the string pointed to by s. The terminating null character is considered to be part of the string; therefore if c is '\0', the functions locate the terminating '\0'.
So, the manpage is basically a copy & paste.
Besides, I suppose that, because of some obfuscated necessity, the second parameter has type int
, but is, in fact, a char
. I think I am not wrong, but can anyone explain to me why is it an int
, not a char
?
If they are both the same, which one is more compatible across versions, and if not, which's the difference?
Description. The strchr() function finds the first occurrence of a character in a string. The character c can be the null character (\0); the ending null character of string is included in the search. The strchr() function operates on null-ended strings.
The index() function locates the first occurrence of c (converted to an unsigned char) in the string pointed to by string. The character c can be the NULL character (\0); the ending NULL is included in the search. The string argument to the function must contain a NULL character (\0) marking the end of the string.
Just subtract the string address from what strchr returns: char *string = "qwerty"; char *e; int index; e = strchr(string, 'e'); index = (int)(e - string); Note that the result is zero based, so in above example it will be 2.
The strchr() function returns a pointer to the first occurrence of character c located within s. If character c does not occur in the string, strchr() returns a null pointer.
strchr()
is part of the C standard library. index()
is a now deprecated POSIX function. The POSIX specification recommends implementing index()
as a macro that expands to a call to strchr()
.
Since index()
is deprecated in POSIX and not part of the C standard library, you should use strchr()
.
The second parameter is of type int
because these functions predate function prototypes. See also https://stackoverflow.com/a/5919802/ for more information on this.
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