Programming Forums > Application Development > C

nnxion · Apr 3rd, 2006, 6:30 AM

Quote:

Originally Posted by grumpy

Incorrect. An assignment is an expression that yields the value assigned.

Isn't that what I said?

It was what I meant. :o

Edit: Ah yeah stupid, '\0' will result in false too of course (as it is 0). Not just only the 'normal' 0.

jim mcnamara · Apr 3rd, 2006, 7:08 AM

Actually C ran mostly on DEC PDP-8 systems at Bell Labs in the beginning. Those had
8K-32K of core.

Anything you could do to make a routine occupy less memory was a good idea.
void functions save two bytes on the stack frame because they don't return a value.

(Toggle Plain Text)

void strcpy(char *dest, char *src)
{
      while((*dest++=*src++) );
}

does it in the least possible amount of memory on a PDP. The implicit non-zero comparison also saves one more - a two byte opcode vs a three byte opcode.

Polyphemus_ · Apr 3rd, 2006, 8:00 AM

I thought functions returned values by putting the return value in the eax register?

grumpy · Apr 3rd, 2006, 8:40 AM

Actually, Jim, very early C did not even have the void keyword. void return types (and void pointers) were originally introduced as an unofficial extension of K&R C by a number of vendors, including AT&T, and eventually found their way into ANSI/ISO C. The reason usually cited for the introduction of void return from functions, as you suggest, was to allow minimisation of memory used when calling/returning from a function.

Polyphemus_ : Placing a return value into the eax register is a convention used by some compilers on particular hardware and OS. It is certainly not universal. Not all machines have an eax register (heck, some machines don't even have registers).

DaWei · Apr 3rd, 2006, 9:01 AM

Storage media didn't have a lot of capacity, either. The first floppies I used were 8-inch, 120K. Digitally recorded cassette tapes were in the 50K - 200K range. Recording density was low enough that one could, using Magnasee, observe individual flux transitions with a 10x loupe or even less.

nnxion · Apr 3rd, 2006, 9:23 AM

Quote:

Originally Posted by DaWei

The first floppies I used were 8-inch, 120K. Digitally recorded cassette tapes were in the 50K - 200K range.

Man, I wish I could go back in time and sell my computer.

jim mcnamara · Apr 3rd, 2006, 11:02 AM

grumpy is correct - the "standard" version of C did not support void to start with.

However, Morristown sent out free Unix and C tapes (you had to return the tape).
By 1980 there were "mixed" versions floating around from umpteen different places like Berkley. We had System VII (yes, Grumpy that's correct) unix on a PDP in 1981(?) for a major parking violations project.

Several of us went to Morristown on a collaborative project, and along the way we picked up crabs. If grumpy was around back then he knows about crabs. It ain't what you think...

grumpy · Apr 4th, 2006, 6:16 AM

May be a bit before my time, Jim. For some reason your post made me think of the Maryland Crab, from an article related to parallel computing I read some years back. My knowledge is definitely not first hand though.

bl00dninja · Apr 5th, 2006, 2:01 AM

lots of interesting replies...thanks!

i think this summer i will go through the k&r and stroustrup's book to get a better handle on things.

Apr 3rd, 2006, 7:08 AM	#12
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	Actually C ran mostly on DEC PDP-8 systems at Bell Labs in the beginning. Those had 8K-32K of core. Anything you could do to make a routine occupy less memory was a good idea. void functions save two bytes on the stack frame because they don't return a value. (Toggle Plain Text) void strcpy(char dest, char src) { while((dest++=src++) ); } void strcpy(char dest, char src) { while((dest++=src++) ); } does it in the least possible amount of memory on a PDP. The implicit non-zero comparison also saves one more - a two byte opcode vs a three byte opcode.

Apr 3rd, 2006, 9:01 AM	#15
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Storage media didn't have a lot of capacity, either. The first floppies I used were 8-inch, 120K. Digitally recorded cassette tapes were in the 50K - 200K range. Recording density was low enough that one could, using Magnasee, observe individual flux transitions with a 10x loupe or even less. __________________ 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

Apr 5th, 2006, 2:01 AM	#19
bl00dninja Programming Guru Join Date: Oct 2004 Location: namespace std Posts: 1,246 Rep Power: 6	lots of interesting replies...thanks! i think this summer i will go through the k&r and stroustrup's book to get a better handle on things. __________________ i put on my robe and wizard hat... Have you ever heard of Plato, Aristotle, Socrates?...Morons.

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Apr 3rd, 2006, 8:00 AM	#13
Polyphemus_ Expert Programmer Join Date: Aug 2005 Location: Rotterdam, the Netherlands Posts: 942 Rep Power: 4	I thought functions returned values by putting the return value in the eax register?

Apr 3rd, 2006, 8:40 AM	#14
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	Actually, Jim, very early C did not even have the void keyword. void return types (and void pointers) were originally introduced as an unofficial extension of K&R C by a number of vendors, including AT&T, and eventually found their way into ANSI/ISO C. The reason usually cited for the introduction of void return from functions, as you suggest, was to allow minimisation of memory used when calling/returning from a function. Polyphemus_ : Placing a return value into the eax register is a convention used by some compilers on particular hardware and OS. It is certainly not universal. Not all machines have an eax register (heck, some machines don't even have registers).

Apr 3rd, 2006, 11:02 AM	#17
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	grumpy is correct - the "standard" version of C did not support void to start with. However, Morristown sent out free Unix and C tapes (you had to return the tape). By 1980 there were "mixed" versions floating around from umpteen different places like Berkley. We had System VII (yes, Grumpy that's correct) unix on a PDP in 1981(?) for a major parking violations project. Several of us went to Morristown on a collaborative project, and along the way we picked up crabs. If grumpy was around back then he knows about crabs. It ain't what you think...

Apr 4th, 2006, 6:16 AM	#18
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	May be a bit before my time, Jim. For some reason your post made me think of the Maryland Crab, from an article related to parallel computing I read some years back. My knowledge is definitely not first hand though.

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Programming Forums > Application Development > C

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