Programming Forums > Application Development > C

Prm753 · Jun 3rd, 2006, 5:32 PM

Hi again.

I have searched high and low for this but have found nothing really pertaining to what I want to do. Is there a function that will let you get at a specified position in a string? Not at the beginning or end, but at say, the middle. For example, if I had the string: "My name is Paul." and I wanted to get to the 6th character, how might I go about doing that if there is no such function to do it? (Without manually changing the string in the compiler)

Thanks in advance.

Jessehk · Jun 3rd, 2006, 5:47 PM

All I could find was a function that returns a pointer to a sub-string.

http://www.cplusplus.com/ref/cstring/strstr.html

Would that help?

Here's an example:

(Toggle Plain Text)

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

int main(void) {
	char str[] = "Hello, world!";

	char *subStr = strstr(str, "world");
	printf("%s, %s\n", "Goodbye", subStr);

	return 0;
}

/* OUTPUT:
 * Goodbye, world!
 */

Animatronic · Jun 3rd, 2006, 6:16 PM

"My name is Paul."[5] returns the sixth character, but maybe notwhat you ment.

Serinth · Jun 3rd, 2006, 6:17 PM

say you had a string str: "foshizzle", why don't you just strlen and then divide that by 2 and then printf str[half the value of strlen]

Adak · Jun 3rd, 2006, 6:38 PM

Quote:

Originally Posted by Prm753

Hi again.

I have searched high and low for this but have found nothing really pertaining to what I want to do. Is there a function that will let you get at a specified position in a string? Not at the beginning or end, but at say, the middle. For example, if I had the string: "My name is Paul." and I wanted to get to the 6th character, how might I go about doing that if there is no such function to do it? (Without manually changing the string in the compiler)

Thanks in advance.

Use pointer arithmetic to increment from the string's base address, up to whatever letter you want.

You're not searching for a substring, just "walking" up the string, right?

Adak

DaWei · Jun 3rd, 2006, 6:44 PM

Your question isn't really clear. That's why all your answerees are saying, "you meant so-and-so, right?) If you mean, find a substring, Jesse has what you need (unless you just want to roll your own). As Animatronic says, if you just want to get at a specified position in a string, what's wrong with myString [specifiedPosition]? If you want to find a character, there are such things as strchr and ilk. Pay no attention to Serinth's solution, which is just trash. I see no reason to use pointer arithmetic to increment a string's pointer up to what you want when you can go straight there, if you know what you want. If you don't know what you want, you're up shit creek, anyway.

Serinth · Jun 3rd, 2006, 6:48 PM

what's wrong with mine? it's basically saying use str[position] like you said.

edit: Yeah it's probably the unclear question :\

DaWei · Jun 3rd, 2006, 6:49 PM

No, it isn't.

jim mcnamara · Jun 5th, 2006, 9:05 AM

Quote:

Originally Posted by DaWei

No, it isn't.

Pending flame war? hope not.

To the OP:
C isn't like VB - it has a limited number of primitive functions. So if you want a substr function you have to write it.

(Toggle Plain Text)

/* 
    this will work only for null terminated strings, and cannot test the size
    of the destination buffer, ie., (you know) len has to be less than the
    # of chars dest can hold.
*/
char *substr(char *dest, char *src, size_t start, size_t len)
{    
    char *p=src;
    char *q=dest;
    size_t i=0;

    while(i<start)
    {
        if(!*p) return dest;
        p++;
        i++;
    }
    for(i=0;i<len && *p;i++) *q++=*p++;
    *q=0x0;
    return dest;
}

http://www.cs.cf.ac.uk/Dave/C/chapter2_21.html
lists functions that most C compilers offer.

DaWei · Jun 5th, 2006, 9:53 AM

Quote:

Pending flame war? hope not.

Quote:

No, it isn't.

The sally wouldn't have been nearly that mild.

Jun 3rd, 2006, 5:32 PM	#1
Prm753 Professional Programmer Join Date: Oct 2005 Location: United States Posts: 447 Rep Power: 4	Getting middle of string Hi again. I have searched high and low for this but have found nothing really pertaining to what I want to do. Is there a function that will let you get at a specified position in a string? Not at the beginning or end, but at say, the middle. For example, if I had the string: "My name is Paul." and I wanted to get to the 6th character, how might I go about doing that if there is no such function to do it? (Without manually changing the string in the compiler) Thanks in advance. __________________ The world's first athletic computer geek! The home of PrProgramsStudios How not to post a question: <-- Please don't reply

Jun 3rd, 2006, 5:47 PM	#2
Jessehk The Oblivious One Join Date: May 2005 Location: Ontario, Canada Posts: 644 Rep Power: 4	All I could find was a function that returns a pointer to a sub-string. http://www.cplusplus.com/ref/cstring/strstr.html Would that help? Here's an example: (Toggle Plain Text) #include <stdio.h> #include <string.h> int main(void) { char str[] = "Hello, world!"; char subStr = strstr(str, "world"); printf("%s, %s\n", "Goodbye", subStr); return 0; } / OUTPUT: * Goodbye, world! / #include <stdio.h> #include <string.h> int main(void) { char str[] = "Hello, world!"; char subStr = strstr(str, "world"); printf("%s, %s\n", "Goodbye", subStr); return 0; } /* OUTPUT: * Goodbye, world! */ __________________ Dr. Zoidberg: [ecstatic] I'm going to a movie... with FRIENDS!

Jun 3rd, 2006, 6:17 PM	#4
Serinth Programmer Join Date: Sep 2005 Posts: 50 Rep Power: 4	say you had a string str: "foshizzle", why don't you just strlen and then divide that by 2 and then printf str[half the value of strlen] __________________ A girl talked to me once. http://www.latestanime.com

Jun 3rd, 2006, 6:44 PM	#6
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Your question isn't really clear. That's why all your answerees are saying, "you meant so-and-so, right?) If you mean, find a substring, Jesse has what you need (unless you just want to roll your own). As Animatronic says, if you just want to get at a specified position in a string, what's wrong with myString [specifiedPosition]? If you want to find a character, there are such things as strchr and ilk. Pay no attention to Serinth's solution, which is just trash. I see no reason to use pointer arithmetic to increment a string's pointer up to what you want when you can go straight there, if you know what you want. If you don't know what you want, you're up shit creek, anyway. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Jun 3rd, 2006, 6:48 PM	#7
Serinth Programmer Join Date: Sep 2005 Posts: 50 Rep Power: 4	what's wrong with mine? it's basically saying use str[position] like you said. edit: Yeah it's probably the unclear question :\ __________________ A girl talked to me once. http://www.latestanime.com

Jun 3rd, 2006, 6:16 PM	#3
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	"My name is Paul."[5] returns the sixth character, but maybe notwhat you ment.

Jun 3rd, 2006, 6:49 PM	#8
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	No, it isn't. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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Programming Forums > Application Development > C

Getting middle of string