Programming Forums > Application Development > C

aznluvsmc · Nov 4th, 2005, 11:21 PM

I'm playing around with some of the string functions to see how they work and I came across this odd problem in my code. The value of i after my while loop exits is reset to 0 even though the last number in the loop is 3. I'm pretty sure that the value should not be 0 but after studying for the last 2 hours I'm not sure if my brain can see the problem. Please help me out.

(Toggle Plain Text)

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

int main(void) {
        char input[21];
        char *name[3];
        int i = 1;

        printf("Please enter you name: ");
        gets(input);

        if ((name[0] = strtok(input, " ")) != NULL) {
                while ((name[i] = strtok(NULL, " ")) != NULL && i < 3) {
                        printf("%d\n", i); /* i is 3 at end of loop when */
                                            /* john jacob smith is entered */
                        i++;
                }
        }

        printf("%d\n", i); /* i is 0 after loop, why? */

        while (--i >= 0) {
                switch (i) {

                        case 0: printf("First Name: %s\n", name[i]);
                                printf("Length: %d\n", strlen(name[i]));
                                break;
                        case 1: printf("Middle Name: %s\n", name[i]);
                                printf("Length: %d\n", strlen(name[i]));
                                break;
                        case 2: printf("Last Name: %s\n", name[i]);
                                printf("Length: %d\n", strlen(name[i]));
                                break;
                }
        }

        return 0;
}

sinix · Nov 5th, 2005, 12:13 AM

what's the function 'strtok()'?I can'tfind it in my man file?

bl00dninja · Nov 5th, 2005, 1:32 AM

i couldn't figure it out either...so i ran it. you can stop scratching your head. it is NOT reset to zero. it prints "1 2 3" where the "3" is the last printf outside of the loop. i modified NOTHING. now you can sleep. :p

aznluvsmc · Nov 5th, 2005, 9:24 AM

Quote:

Originally Posted by sinix

what's the function 'strtok()'?I can'tfind it in my man file?

strtok() is part of <string.h>. It takes a string and splits it into tokens on any character speficied in string2.

Quote:

Originally Posted by bl00dninja

i couldn't figure it out either...so i ran it. you can stop scratching your head. it is NOT reset to zero. it prints "1 2 3" where the "3" is the last printf outside of the loop. i modified NOTHING. now you can sleep. :p

That's odd. I decided to delete my old file and just copy what I posted into a new one a run it. It still prints "1 2 0". Maybe it's because I'm running the code on AIX? I'll test it on Linux to see if it makes a difference.

aznluvsmc · Nov 5th, 2005, 5:29 PM

So I ran the code on my college's Linux server and it works properly. I guess there's some funky stuff between the gcc compiler and the AIX compiler.

DaWei · Nov 5th, 2005, 6:45 PM

For those who haven't used "strtok", be aware that it works with a static pointer (to keep track between calls) and modifies the original string (dumps terminators into it). Be sure and copy the original string if you want to preserve it.

aznluvsmc · Nov 5th, 2005, 9:58 PM

Quote:

Originally Posted by DaWei

Be sure and copy the original string if you want to preserve it.

Yes, I had to learn this the hard way.

DaWei · Nov 6th, 2005, 7:03 AM

Actually, you could have just read the docs, but I figured (how did I guess?) a lot of people don't.

Polyphemus_ · Nov 6th, 2005, 7:05 AM

I've read the docs

*proud*

aznluvsmc · Nov 6th, 2005, 11:29 AM

Actually, I never heard of strtok() until Friday when one of my professors mentioned it. I checked it in my book The C Programming Language and followed that documentation.

Nov 4th, 2005, 11:21 PM	#1
aznluvsmc Hobbyist Programmer Join Date: Aug 2005 Posts: 137 Rep Power: 4	Value of index incorrect after loop I'm playing around with some of the string functions to see how they work and I came across this odd problem in my code. The value of i after my while loop exits is reset to 0 even though the last number in the loop is 3. I'm pretty sure that the value should not be 0 but after studying for the last 2 hours I'm not sure if my brain can see the problem. Please help me out. (Toggle Plain Text) #include <stdio.h> #include <string.h> int main(void) { char input[21]; char name[3]; int i = 1; printf("Please enter you name: "); gets(input); if ((name[0] = strtok(input, " ")) != NULL) { while ((name[i] = strtok(NULL, " ")) != NULL && i < 3) { printf("%d\n", i); / i is 3 at end of loop when / / john jacob smith is entered / i++; } } printf("%d\n", i); / i is 0 after loop, why? / while (--i >= 0) { switch (i) { case 0: printf("First Name: %s\n", name[i]); printf("Length: %d\n", strlen(name[i])); break; case 1: printf("Middle Name: %s\n", name[i]); printf("Length: %d\n", strlen(name[i])); break; case 2: printf("Last Name: %s\n", name[i]); printf("Length: %d\n", strlen(name[i])); break; } } return 0; } #include <stdio.h> #include <string.h> int main(void) { char input[21]; char name[3]; int i = 1; printf("Please enter you name: "); gets(input); if ((name[0] = strtok(input, " ")) != NULL) { while ((name[i] = strtok(NULL, " ")) != NULL && i < 3) { printf("%d\n", i); /* i is 3 at end of loop when / / john jacob smith is entered / i++; } } printf("%d\n", i); / i is 0 after loop, why? */ while (--i >= 0) { switch (i) { case 0: printf("First Name: %s\n", name[i]); printf("Length: %d\n", strlen(name[i])); break; case 1: printf("Middle Name: %s\n", name[i]); printf("Length: %d\n", strlen(name[i])); break; case 2: printf("Last Name: %s\n", name[i]); printf("Length: %d\n", strlen(name[i])); break; } } return 0; }

Nov 5th, 2005, 1:32 AM	#3
bl00dninja Programming Guru Join Date: Oct 2004 Location: namespace std Posts: 1,246 Rep Power: 5	i couldn't figure it out either...so i ran it. you can stop scratching your head. it is NOT reset to zero. it prints "1 2 3" where the "3" is the last printf outside of the loop. i modified NOTHING. now you can sleep. :p __________________ i put on my robe and wizard hat... Have you ever heard of Plato, Aristotle, Socrates?...Morons.

Nov 5th, 2005, 6:45 PM	#6
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	For those who haven't used "strtok", be aware that it works with a static pointer (to keep track between calls) and modifies the original string (dumps terminators into it). Be sure and copy the original string if you want to preserve it. __________________ 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

Nov 6th, 2005, 7:03 AM	#8
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Actually, you could have just read the docs, but I figured (how did I guess?) a lot of people don'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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Nov 5th, 2005, 12:13 AM	#2
sinix Programmer Join Date: Nov 2005 Location: China Posts: 47 Rep Power: 0	what's the function 'strtok()'?I can'tfind it in my man file?

Nov 5th, 2005, 5:29 PM	#5
aznluvsmc Hobbyist Programmer Join Date: Aug 2005 Posts: 137 Rep Power: 4	So I ran the code on my college's Linux server and it works properly. I guess there's some funky stuff between the gcc compiler and the AIX compiler.

Nov 6th, 2005, 7:05 AM	#9
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	I've read the docs proud

Nov 6th, 2005, 11:29 AM	#10
aznluvsmc Hobbyist Programmer Join Date: Aug 2005 Posts: 137 Rep Power: 4	Actually, I never heard of strtok() until Friday when one of my professors mentioned it. I checked it in my book The C Programming Language and followed that documentation.

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Programming Forums > Application Development > C

Value of index incorrect after loop