a little help!

jonathanrs · 07-30-2009, 12:14 AM

i'm new to programming and i was trying to compile this code:

usage: as.exe value1 value2 value3

Code:

if(argv[2]=="x"){
printf("worked\n");
}else{printf("not worked\n");}

but it always show me it worked!
=P

does any one can help me on this?

thanks

**laserlight** · 07-30-2009, 12:23 AM

Post the smallest and simplest compilable program that demonstrates the problem.

Sebastiani · 07-30-2009, 01:20 AM

Quote:

Originally Posted by jonathanrs

i'm new to programming and i was trying to compile this code:

usage: as.exe value1 value2 value3

Code:

if(argv[2]=="x"){
printf("worked\n");
}else{printf("not worked\n");}

but it always show me it worked!
=P

does any one can help me on this?

thanks

You need to use strcmp to compare strings. Even so, the test should have failed since argv[2] most certainly does not have the same address as the string literal.

slingerland3g · 07-30-2009, 08:00 AM

What Sebastiani stated, but on a tangent you may want to review the use of getopt().

Example of Getopt - The GNU C Library

jonathanrs · 07-30-2009, 08:41 PM

sorry people! something really weird happened to this computer while trying to compile this code, or it just didn't want to follow my commands. =P

i'd tried everything and this:

Code:

if(strcmp(argv[2],"x")==FALSE) {
printf("worked");}else{printf("error");}

always returned true! but today i've compiled this code again and it worked! o0

thanks ^^

Sebastiani · 07-30-2009, 08:45 PM

>> always returned true! but today i've compiled this code again and it worked! o0

Post the entire program. And strcmp doesn't return false/true. Always be sure to read the documentation before attempting to use any function/library.

jonathanrs · 08-01-2009, 02:58 PM

Code:

main()
{
char var[8]="abcdefgh";

if(strcmp(var,"abcdefgh")==1){printf("true\n");
system("pause");
}else{printf("false\n");system("pause");}

}

When i said it always returned true, i was talking about 1 and 0.The function returns an int. That's the code. If i change the size of var,for ex. var[10]="abcdefgh", the strcmp() function will give me printf("false");

thanks

nonoob · 08-01-2009, 03:08 PM

Um, strcmp() returns negative integer, zero (0), or a positive integer depending on how its two arguments compare with each other... i.e. A < B, A ==B, or A > B respectively.

The way you've coded it, you are interpreting a +1 as "true". When A > B you could get any positive integer - not necessarily limited to +1.
Perhaps you are getting your "false" because the strings are indeed equal.

You should probably allow for the null terminator - so do var[9]. I'm surprised the compiler didn't whine.

Elysia · 08-01-2009, 03:18 PM

It's actually valid to put a string without a string literal into an array in C, so it's no wonder it doesn't complain.
However, you must ALWAYS null terminate strings if you want to use string functions with it. Don't specify the size; instead, let the compiler figure it out:

Code:

char str[] = "My string";

Also, main must return int.

07-30-2009, 12:14 AM	#1
jonathanrs Registered User Join Date: Jul 2009 Posts: 3	a little help! i'm new to programming and i was trying to compile this code: usage: as.exe value1 value2 value3 Code: if(argv[2]=="x"){ printf("worked\n"); }else{printf("not worked\n");} but it always show me it worked! =P does any one can help me on this? thanks
jonathanrs is offline

07-30-2009, 12:23 AM	#2
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,368	Post the smallest and simplest compilable program that demonstrates the problem. __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
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07-30-2009, 08:00 AM	#4
slingerland3g Registered User Join Date: Jan 2008 Location: Seattle Posts: 476	What Sebastiani stated, but on a tangent you may want to review the use of getopt(). Example of Getopt - The GNU C Library
slingerland3g is offline

07-30-2009, 08:41 PM	#5
jonathanrs Registered User Join Date: Jul 2009 Posts: 3	thanks sorry people! something really weird happened to this computer while trying to compile this code, or it just didn't want to follow my commands. =P i'd tried everything and this: Code: if(strcmp(argv[2],"x")==FALSE) { printf("worked");}else{printf("error");} always returned true! but today i've compiled this code again and it worked! o0 thanks ^^
jonathanrs is offline

07-30-2009, 08:45 PM	#6
Sebastiani Guest Join Date: Aug 2001 Posts: 4,923	>> always returned true! but today i've compiled this code again and it worked! o0 Post the entire program. And strcmp doesn't return false/true. Always be sure to read the documentation before attempting to use any function/library.
Sebastiani is offline

08-01-2009, 02:58 PM	#7
jonathanrs Registered User Join Date: Jul 2009 Posts: 3	sorry Code: main() { char var[8]="abcdefgh"; if(strcmp(var,"abcdefgh")==1){printf("true\n"); system("pause"); }else{printf("false\n");system("pause");} } When i said it always returned true, i was talking about 1 and 0.The function returns an int. That's the code. If i change the size of var,for ex. var[10]="abcdefgh", the strcmp() function will give me printf("false"); thanks
jonathanrs is offline

08-01-2009, 03:08 PM	#8
nonoob Registered User Join Date: Sep 2008 Location: Toronto, Canada Posts: 507	Um, strcmp() returns negative integer, zero (0), or a positive integer depending on how its two arguments compare with each other... i.e. A < B, A ==B, or A > B respectively. The way you've coded it, you are interpreting a +1 as "true". When A > B you could get any positive integer - not necessarily limited to +1. Perhaps you are getting your "false" because the strings are indeed equal. You should probably allow for the null terminator - so do var[9]. I'm surprised the compiler didn't whine. Last edited by nonoob; 08-01-2009 at 03:14 PM.
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