Programming Forums > Application Development > C

aznluvsmc · Aug 16th, 2005, 8:36 PM

Hi,

I'd like to know why assigning a value to char using an octal value sometimes gives a warning message causing incorrect output.

Please look at the following code:

(Toggle Plain Text)

int main(void)
   {
   char c = '\074', d = '\0101', e = '\101';

   printf("c is %c d is %c e is %c", c, d, e);

   return 0;
   }

Here c is assigned the character "<" but d gives a warning on compile and will be displayed as the character "1" where as e displays "A". I don't understand why I can have a leading 0 inconjunction with the "\" character sometimes and not other times.

I could just assign the values with leading zeroes and take away the "\" and single quotes but I'd just like to understand my problem to better understand C.

DaWei · Aug 16th, 2005, 9:26 PM

An ASCII character in octal notation may only have 3 digits.

aznluvsmc · Aug 16th, 2005, 9:49 PM

Alright, simple and straight to the point explanation. My C Primer Plus book didn't explicity state this. Thanks!

Ooble · Aug 17th, 2005, 9:22 AM

Out of curiosity, how does the compiler differ between "\074", meaning octal character 74, and "\074", meaning a null byte followed by the characters '7' and '4'?

Monster · Aug 17th, 2005, 2:15 PM

Quote:

Originally Posted by Ooble

Out of curiosity, how does the compiler differ between "\074", meaning octal character 74, and "\074", meaning a null byte followed by the characters '7' and '4'?

Single quotes = octal number
Double quotes = string

grumpy · Aug 18th, 2005, 2:06 AM

Quote:

Originally Posted by Ooble

Out of curiosity, how does the compiler differ between "\074", meaning octal character 74, and "\074", meaning a null byte followed by the characters '7' and '4'?

If you intend to have a null byte followed by 7 and 4, you have to tell the compiler that, viz "\00074". The first three zeros after the backslash are interpreted to mean the null byte.

DaWei · Aug 18th, 2005, 5:31 AM

377 IS highest for a byte, yes, and the "unfulfilled" nature is, to me, one of the drawbacks of octal notation. Address busses aren't limited to 8 bits, though. Twelve bits were common at one time, which fills up nicely. Hex became more common when the busses went to 16.

Ooble · Aug 17th, 2005, 6:03 PM

I got that. What I want to know is how you insert characters represented as octal numbers into a string.

Scorpions4ever · Aug 17th, 2005, 7:15 PM

Quote:

Originally Posted by Ooble

I got that. What I want to know is how you insert characters represented as octal numbers into a string.

(Toggle Plain Text)

printf("This is the first letter of the alphabet: \101\n");

Works for me on gcc 3.3.3

Navid · Aug 17th, 2005, 8:15 PM

This is the first time i've ever seen ooble asking a question...

I got a question too, why is their an octal format and hex format when you can use the decimal format?

Aug 16th, 2005, 8:36 PM	#1
aznluvsmc Hobbyist Programmer Join Date: Aug 2005 Posts: 137 Rep Power: 4	Char assignment using Octal values Hi, I'd like to know why assigning a value to char using an octal value sometimes gives a warning message causing incorrect output. Please look at the following code: (Toggle Plain Text) int main(void) { char c = '\074', d = '\0101', e = '\101'; printf("c is %c d is %c e is %c", c, d, e); return 0; } int main(void) { char c = '\074', d = '\0101', e = '\101'; printf("c is %c d is %c e is %c", c, d, e); return 0; } Here c is assigned the character "<" but d gives a warning on compile and will be displayed as the character "1" where as e displays "A". I don't understand why I can have a leading 0 inconjunction with the "\" character sometimes and not other times. I could just assign the values with leading zeroes and take away the "\" and single quotes but I'd just like to understand my problem to better understand C.

Aug 16th, 2005, 9:26 PM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	An ASCII character in octal notation may only have 3 digits. __________________ 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

Aug 17th, 2005, 9:22 AM	#4
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	Out of curiosity, how does the compiler differ between "\074", meaning octal character 74, and "\074", meaning a null byte followed by the characters '7' and '4'? __________________ Me :: You :: Them

Aug 18th, 2005, 5:31 AM	#7
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	377 IS highest for a byte, yes, and the "unfulfilled" nature is, to me, one of the drawbacks of octal notation. Address busses aren't limited to 8 bits, though. Twelve bits were common at one time, which fills up nicely. Hex became more common when the busses went to 16. __________________ 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

Aug 17th, 2005, 6:03 PM	#8
Ooble I eat cake for breakfast. Join Date: Jul 2004 Location: In my box. Posts: 4,434 Rep Power: 9	I got that. What I want to know is how you insert characters represented as octal numbers into a string. __________________ Me :: You :: Them

Aug 16th, 2005, 9:49 PM	#3
aznluvsmc Hobbyist Programmer Join Date: Aug 2005 Posts: 137 Rep Power: 4	Alright, simple and straight to the point explanation. My C Primer Plus book didn't explicity state this. Thanks!

Aug 17th, 2005, 8:15 PM	#10
Navid Hobbyist Programmer Join Date: Feb 2005 Location: Canada Posts: 187 Rep Power: 4	This is the first time i've ever seen ooble asking a question... I got a question too, why is their an octal format and hex format when you can use the decimal format?

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Programming Forums > Application Development > C

Char assignment using Octal values