C Language, int func(int) versus int func(int *) efficacy.

int func(int) versus int func(int *) efficacy.

Author	Message
Ori Gi #1 / 11	int func(int) versus int func(int ) efficacy. Hello, I am not a professional programmer. I have been told that the function: ' int func(int) ' is faster then the function ' int func(int ) ' . Obviously, both functions do the same. If anybody knows why, I will appreciate the answer. Thank You Very Much,
Mon, 19 Mar 2001 03:00:00 GMT

Ben Pfaf #2 / 11	int func(int) versus int func(int ) efficacy. I have been told that the function: ' int func(int) ' is faster then the function ' int func(int ) ' . Obviously, both functions do the same. No, they do not do the same thing. The former takes an int argument, the latter takes a pointer to int argument. -- (supporter of the campaign for grumpiness where grumpiness is due in c.l.c) Please: do not email me copies of your posts to comp.lang.c do not ask me C questions via email; post them instead
Mon, 19 Mar 2001 03:00:00 GMT

Russell Harpe #3 / 11	int func(int) versus int func(int ) efficacy. See below for comments -RH- ... Ori Gill wrote ... ... Quote: >I have been told that the function: ' int func(int) ' is faster then >the function ' int func(int ) ' . -RH- Depends on the function. I think what the individual means is that using 'n' versus '*pn' is faster. I suppose it would be, but in many cases you need the address of the variable and not just what it is. Quote: >Obviously, both functions do the same. -RH- Depends on the function. The easiest way to see the difference is to write your own and try them out. ...
Mon, 19 Mar 2001 03:00:00 GMT

User9230 #4 / 11	int func(int) versus int func(int ) efficacy. Ori: Quote: >Hello, >I am not a professional programmer. >I have been told that the function: ' int func(int) ' is faster then >the function ' int func(int ) ' . Either it is faster, slower or the same. That's called trichotomy. Quote: >Obviously, both functions do the same. Sort of. Both can accomplish the same purpose, perhaps. Quote: >If anybody knows why, I will appreciate the answer. Why? You mean why pass an address rather than the value? The answer is not for speed, either way. You pass the address if you are going to change the contents of the variable in the called function, and you want it to change in the routine that calls the function also. If you just want the value passed, then you don't use an address. Someone who passes the address because they think it is faster is incompetent and needs further training. Quote: >Thank You Very Much, You're double-extra peachy welcome. -- C-FAQ ftp sites: ftp://ftp.eskimo.com ftp://rtfm.mit.edu Hypertext C-FAQ: http://www.eskimo.com/~scs/C-faq/top.html C-FAQ Book: ISBN 0-201-84519-9. Want Software? Algorithms? Pubs? http://www.infoseek.com
Tue, 20 Mar 2001 03:00:00 GMT

Joe Mau #5 / 11	int func(int) versus int func(int *) efficacy. Quote: > Why? You mean why pass an address rather than the value? The answer is not > for speed, either way. You pass the address if you are going to change the > contents of the variable in the called function, and you want it to change in > the routine that calls the function also. If you just want the value passed, > then you don't use an address. Someone who passes the address because they > think it is faster is incompetent and needs further training. It should be clarified that this statement only applies to types such as int. For large user defined types, it is usually more efficient to use pointers rather than copying large amounts of data to/from functions. -- Joe
Tue, 20 Mar 2001 03:00:00 GMT

Ori Gil #6 / 11	int func(int) versus int func(int ) efficacy. Hello, I know that... I meant to say that both functions are used for the same _purpose_ . Quote: > I have been told that the function: ' int func(int) ' is faster then > the function ' int func(int ) ' . > Obviously, both functions do the same. > No, they do not do the same thing. The former takes an int argument, > the latter takes a pointer to int argument. > -- > (supporter of the campaign for grumpiness where grumpiness is due in c.l.c) > Please: do not email me copies of your posts to comp.lang.c > do not ask me C questions via email; post them instead
Tue, 20 Mar 2001 03:00:00 GMT

Ori Gil #7 / 11	int func(int) versus int func(int ) efficacy. Hello again, " -RH- Depends on the function. I think what the individual means is that using 'n' versus 'pn' is faster. I suppose it would be, but in many cases you need the address of the variable and not just what it is. " This is exactly what I meant, and by the time I am sending this message no reply answered the question. I know when I should pass a pointer to a variable or when to pass the variable's value, and I am sorry if I failed to explain the question. I asked the question just because I am curious: Why transferring an ' int ' ("int variable") is faster then transferring a pointer to ' int '(" int p_variable") ? In both cased the function returns an 'int' : Calling to int func(int) is faster then to int func(int ) . If any body knows the technical reason to this specific question, I will be happy to hear about it. Thanks again, Ori Gill Quote: > See below for comments -RH- ... > Ori Gill wrote ... > ... > >I have been told that the function: ' int func(int) ' is faster then > >the function ' int func(int ) ' . > -RH- Depends on the function. I think what the individual means is that > using 'n' versus 'pn' is faster. I suppose it would be, but in many cases > you need the address of the variable and not just what it is. > >Obviously, both functions do the same. > -RH- Depends on the function. The easiest way to see the difference is to > write your own and try them out. > ...
Tue, 20 Mar 2001 03:00:00 GMT

Dan P #8 / 11	int func(int) versus int func(int ) efficacy. Quote: >Why transferring an ' int ' ("int variable") is faster then transferring a >pointer to ' int '(" int p_variable") ? >In both cased the function returns an 'int' : >Calling to int func(int) is faster then to int func(int *) . >If any body knows the technical reason to this specific question, I will >be happy to hear about it. I don't think that the calling sequence is faster in one case than the other. But the function itself can be better optimized if it takes an int argument instead of an int pointer argument. Pointers are great for flexibility, but they restrict the number of safe optimizations that the compiler can perform. Moreover, accessing a variable thru a pointer is usually slower, because it takes an additional memory accesses. Bottom line: use pointers only if and when you have to. Dan -- Dan Pop CERN, IT Division Mail: CERN - EP, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland
Tue, 20 Mar 2001 03:00:00 GMT

Stephan Wilm #9 / 11	int func(int) versus int func(int ) efficacy. Quote: > I am not a professional programmer. > I have been told that the function: ' int func(int) ' is faster then > the function ' int func(int ) ' . Hi Ori Gill, Please drop this idea. If there is a difference at all, it is very very small. And it will totally compiler dependant. I.e. on compiler A the first might be 5 microseconds faster and on compiler B it's 7 microseconds slower. Quote: > Obviously, both functions do the same. No, they do not. The first function get's an integer and the second function receives an pointer to an integer. Stephan (initiator of the campaign against grumpiness in c.l.c)
Tue, 20 Mar 2001 03:00:00 GMT

Craig Franc #10 / 11	int func(int) versus int func(int ) efficacy. Quote: >I asked the question just because I am curious: >Why transferring an ' int ' ("int variable") is faster then transferring a >pointer to ' int '(" int p_variable") ? >In both cased the function returns an 'int' : >Calling to int func(int) is faster then to int func(int ) . >If any body knows the technical reason to this specific question, I will >be happy to hear about it. It may be on a particular platform the code that handles the arguments is less efficient with one or the other. One thing to note is that to use the value of the int argument, code will probably be generated to fetch the value at the address that was passed. That's an extra step that doesn't have to be performed if the value is passed directly. -- Craig Manchester, NH The most savage controversies are those about matters as to which there is no good evidence either way. -- Bertrand Russell
Tue, 20 Mar 2001 03:00:00 GMT

Dann Corbi #11 / 11	int func(int) versus int func(int *) efficacy. Quote: >> Why? You mean why pass an address rather than the value? The answer is not >> for speed, either way. You pass the address if you are going to change the >> contents of the variable in the called function, and you want it to change in >> the routine that calls the function also. If you just want the value passed, >> then you don't use an address. Someone who passes the address because they >> think it is faster is incompetent and needs further training. >It should be clarified that this statement only applies to types such as >int. For large user defined types, it is usually more efficient to use >pointers rather than copying large amounts of data to/from functions. I am of the opinion that unless the data object is simply enormous or there is a proven bottleneck, this aspect should be less of a concern today than it was 20 years ago. Passing by value is a very good protection from corrupting your data. Passing by address may be faster for large objects, but it is still dangerous. I design for "by value" when I want to pass the value. Then, if a profile session shows that a nested function call is a bottleneck, I will change -- reluctantly -- to by address. -- Hypertext C-FAQ: http://www.eskimo.com/~scs/C-faq/top.html C-FAQ ftp: ftp://rtfm.mit.edu, C-FAQ Book: ISBN 0-201-84519-9 Try "C Programming: A Modern Approach" ISBN 0-393-96945-2 Want Software? Algorithms? Pubs? http://www.infoseek.com
Tue, 20 Mar 2001 03:00:00 GMT

Page 1 of 1

[ 11 post ]