atoi()

**Jonathan Turkanis** · Jul 22 '05, 05:16 AM

Re: atoi()

"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in
message news:bu6uga$rjv $1@chessie.cirr .com...[color=blue]
> What is the preferred C++ alternative to C's atoi(), if there is[/color]
one?[color=blue]
>
> --
> Christopher Benson-Manica | I *should* know what I'm talking[/color]
about - if I[color=blue]
> ataru(at)cybers pace.org | don't, I need to know. Flames welcome.[/color]

The standard alternative is to construct a stringstream and read its
data into an int using >>. See also
http://www.boost.org/libs/conversion/lexical_cast.htm.

Jonathan

**Christopher Benson-Manica** · Jul 22 '05, 05:16 AM

Re: atoi()

Jonathan Turkanis <technews@kanga roologic.com> spoke thus:
[color=blue]
> The standard alternative is to construct a stringstream and read its
> data into an int using >>.[/color]

You would recommend such an approach in the following situation?

#include <cstdlib>

int main( int argc, char *argv[] )
{
int count=0;
if( argc > 1 ) {
count=atoi( argv[1] ); // <- worth setting up a stringstream?
}
return EXIT_SUCCESS;
}

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

**Kevin Goodsell** · Jul 22 '05, 05:16 AM

Re: atoi()

Christopher Benson-Manica wrote:[color=blue]
> Jonathan Turkanis <technews@kanga roologic.com> spoke thus:
>
>[color=green]
>>The standard alternative is to construct a stringstream and read its
>>data into an int using >>.[/color]
>
>
> You would recommend such an approach in the following situation?
>
> #include <cstdlib>
>
> int main( int argc, char *argv[] )
> {
> int count=0;
> if( argc > 1 ) {
> count=atoi( argv[1] ); // <- worth setting up a stringstream?[/color]

You forgot std::.
[color=blue]
> }
> return EXIT_SUCCESS;
> }
>[/color]

Well, atoi() doesn't allow much in the way of error detection &
recovery. It silently invokes undefined behavior on overflow, if I
recall correctly. I'd recommend using either the stringstream method or
possibly strtol() or a related function - whichever you think is
appropriate for the situation.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

**Jonathan Turkanis** · Jul 22 '05, 05:16 AM

Re: atoi()

"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in
message news:bu705v$rnu $1@chessie.cirr .com...[color=blue]
> Jonathan Turkanis <technews@kanga roologic.com> spoke thus:
>[color=green]
> > The standard alternative is to construct a stringstream and read[/color][/color]
its[color=blue][color=green]
> > data into an int using >>.[/color]
>
> You would recommend such an approach in the following situation?
>
> #include <cstdlib>
>
> int main( int argc, char *argv[] )
> {
> int count=0;
> if( argc > 1 ) {
> count=atoi( argv[1] ); // <- worth setting up a stringstream?
> }
> return EXIT_SUCCESS;
> }
>[/color]

int main( int argc, char *argv[] )
{
int count=0;
if( argc > 1 && (std::stringstr eam(argv[1]) >> count) )
/* ... */
}
return EXIT_SUCCESS;
}

There is a certain overhead to using a stringstream or stringbuf:
constuction of a locale, and depending on the implementation,
initialization of a number of member pointers and possibly a
synchronization construct. So its not appropriate always. It is,
however, the 'standard C++ alternative.'

Jonathan

**Ron Natalie** · Jul 22 '05, 05:16 AM

Re: atoi()

"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in message news:bu6uga$rjv $1@chessie.cirr .com...[color=blue]
> What is the preferred C++ alternative to C's atoi(), if there is one?
>[/color]
I won't even use atoi in C. There are input conditions that cause it to
invoke undefined behavior. strtol is much better behaved.

**Norbert Riedlin** · Jul 22 '05, 05:16 AM

Re: atoi()

"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> schrieb im
Newsbeitrag news:bu705v$rnu $1@chessie.cirr .com...[color=blue]
> Jonathan Turkanis <technews@kanga roologic.com> spoke thus:
>
> #include <cstdlib>
>
> int main( int argc, char *argv[] )
> {
> int count=0;
> if( argc > 1 ) {
> count=atoi( argv[1] ); // <- worth setting up a stringstream?
> }
> return EXIT_SUCCESS;
> }
>[/color]

What is the difference?

#include <boost/lexical_cast.hp p> // #include <cstdlib>

int main( int argc, char *argv[] )
{
int count=0;
if( argc > 1 ) {
count = boost::lexical_ cast<int>(argv[1]); // count=atoi( argv[1] );
}
// return EXIT_SUCCESS;
}

Why should one _not_ use lexical_cast in this/any case? Ok, to
have the same result here you had to surround the cast by a try
block, catching the appropriate boost::bad_lexi cal_cast but...

In my opinion, lexical_cast is to be preferred in _any_ realistical
case. In not realistical cases, noone cares.

Bye

Norbert

**Jonathan Turkanis** · Jul 22 '05, 05:16 AM

Re: atoi()

"Norbert Riedlin" <norbert.riedli n@t-online.de> wrote in message
news:bu74gg$a6q $06$1@news.t-online.com...[color=blue]
> "Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> schrieb im
> Newsbeitrag news:bu705v$rnu $1@chessie.cirr .com...[color=green]
> > Jonathan Turkanis <technews@kanga roologic.com> spoke thus:
> >
> > #include <cstdlib>
> >
> > int main( int argc, char *argv[] )
> > {
> > int count=0;
> > if( argc > 1 ) {
> > count=atoi( argv[1] ); // <- worth setting up a stringstream?
> > }
> > return EXIT_SUCCESS;
> > }
> >[/color]
>
> What is the difference?
>
> #include <boost/lexical_cast.hp p> // #include <cstdlib>
>
> int main( int argc, char *argv[] )
> {
> int count=0;
> if( argc > 1 ) {
> count = boost::lexical_ cast<int>(argv[1]); // count=atoi([/color]
argv[1] );[color=blue]
> }
> // return EXIT_SUCCESS;
> }
>
> Why should one _not_ use lexical_cast in this/any case? Ok, to
> have the same result here you had to surround the cast by a try
> block, catching the appropriate boost::bad_lexi cal_cast but...
>
> In my opinion, lexical_cast is to be preferred in _any_ realistical
> case. In not realistical cases, noone cares.
>[/color]

Do we disagree on anything? I mentioned the 'standard C++ alternative'
as well as boost::lexical cast; I did not express any preference.

Jonathan

**Norbert Riedlin** · Jul 22 '05, 05:16 AM

Re: atoi()

"Jonathan Turkanis" <technews@kanga roologic.com> schrieb im Newsbeitrag
news:bu74qk$ebe 1i$1@ID-216073.news.uni-berlin.de...[color=blue]
> "Norbert Riedlin" <norbert.riedli n@t-online.de> wrote in message
> news:bu74gg$a6q $06$1@news.t-online.com...[color=green]
> > "Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> schrieb im
> > Newsbeitrag news:bu705v$rnu $1@chessie.cirr .com...[/color]
>
>
> Do we disagree on anything? I mentioned the 'standard C++ alternative'
> as well as boost::lexical cast; I did not express any preference.
>
> Jonathan
>[/color]
Not at all. If you look closer, I was relying to Christopher's post. I
should have
been more careful cutting the posting though...

Bye

Norbert

**Peter Koch Larsen** · Jul 22 '05, 05:17 AM

Re: atoi()

"Norbert Riedlin" <norbert.riedli n@t-online.de> skrev i en meddelelse
news:bu74gg$a6q $06$1@news.t-online.com...[color=blue]
> "Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> schrieb im
> Newsbeitrag news:bu705v$rnu $1@chessie.cirr .com...[color=green]
> > Jonathan Turkanis <technews@kanga roologic.com> spoke thus:
> >
> > #include <cstdlib>
> >
> > int main( int argc, char *argv[] )
> > {
> > int count=0;
> > if( argc > 1 ) {
> > count=atoi( argv[1] ); // <- worth setting up a stringstream?
> > }
> > return EXIT_SUCCESS;
> > }
> >[/color]
>
> What is the difference?
>
> #include <boost/lexical_cast.hp p> // #include <cstdlib>
>
> int main( int argc, char *argv[] )
> {
> int count=0;
> if( argc > 1 ) {
> count = boost::lexical_ cast<int>(argv[1]); // count=atoi( argv[1] );
> }
> // return EXIT_SUCCESS;
> }
>
> Why should one _not_ use lexical_cast in this/any case? Ok, to
> have the same result here you had to surround the cast by a try
> block, catching the appropriate boost::bad_lexi cal_cast but...
>
> In my opinion, lexical_cast is to be preferred in _any_ realistical
> case. In not realistical cases, noone cares.
>
> Bye
>
> Norbert
>[/color]

While I would agree with you in the general case, there could be cases where
avoiding streams would better be avoided. One example is when you write a
program where you are concerned about its footprint: if that program only
uses streams this one place, it does justify using an alternative approach.

Kind regards
Peter

**Nick Hounsome** · Jul 22 '05, 05:17 AM

Re: atoi()

"Christophe r Benson-Manica" <ataru@nospam.c yberspace.org> wrote in message
news:bu6uga$rjv $1@chessie.cirr .com...[color=blue]
> What is the preferred C++ alternative to C's atoi(), if there is one?
>[/color]

- std::atoi is standard C++
- std::strtol is also standard C and standard C++ and is superior in every
respect ( IMHO atoi should be deprecated ).
- You could use an istrstream but why bother?
- I can think of no good reason to use an istringstream if you have a char*.

- as far as I am aware there is no stream equivalent of the strtol ability
to read numbers in decimal,octal or hex

[color=blue]
> --
> Christopher Benson-Manica | I *should* know what I'm talking about - if I
> ataru(at)cybers pace.org | don't, I need to know. Flames welcome.[/color]

**Jeff Schwab** · Jul 22 '05, 05:17 AM

Re: atoi()

Christopher Benson-Manica wrote:[color=blue]
> What is the preferred C++ alternative to C's atoi(), if there is one?
>[/color]

I rolled my own alternative. The idea is this, but if you're looking
for an improvement over atoi, you might consider validating the pointer,
the base, and the digits.

template< typename N > // unsigned numeric type
N ato( char const* p, unsigned base =10 )
{
N result = N( );

while( *p )
{
result = result * base + ( *p <= '9' ? *p - '0' : *p - 'a' + 10 );
++p;
}

return result;
}

#include <iostream>

int main( int argc, char *argv[] )
{
if( argc > 1 )
{
unsigned base = 10;

if( argc > 2 )
{
base = ato< unsigned >( argv[ 2 ] );
}

std::cout << ato< int >( argv[ 1 ], base ) << '\n';
}
}

**Ron Natalie** · Jul 22 '05, 05:18 AM

Re: atoi()

"Nick Hounsome" <nh002@blueyond er.co.uk> wrote in message news:zTPNb.2642 $pD3.311@news-binary.blueyond er.co.uk...[color=blue]
> - std::strtol is also standard C and standard C++ and is superior in every
> respect ( IMHO atoi should be deprecated ).[/color]

In my opinion, it could just be fixed by requiring it to be defined as:
int atoi(const char* s) { return strtol(s, 0, 10); }

That is, change it from undefined behavior to implementation defined value on
overflow. C99 even includes the above snippet as the definition "except for error
behavior."

**Norbert Riedlin** · Jul 22 '05, 05:18 AM

Re: atoi()

"Jeff Schwab" <jeffplus@comca st.net> schrieb im Newsbeitrag
news:o5-dnXnXd-tgfZrdRVn-jQ@comcast.com. ..[color=blue]
> template< typename N > // unsigned numeric type
> N ato( char const* p, unsigned base =10 )
> {
> N result = N( );
>
> while( *p )
> {
> result = result * base + ( *p <= '9' ? *p - '0' : *p - 'a' + 10 );
> ++p;
> }
>
> return result;
> }
>[/color]
You are asuming the ASCII character set? In EBCDIC '9' > 'a'.

Bye

Norbert

**Jeff Schwab** · Jul 22 '05, 05:19 AM

Re: atoi()

Norbert Riedlin wrote:[color=blue]
> "Jeff Schwab" <jeffplus@comca st.net> schrieb im Newsbeitrag
> news:o5-dnXnXd-tgfZrdRVn-jQ@comcast.com. ..
>[color=green]
>>template< typename N > // unsigned numeric type
>>N ato( char const* p, unsigned base =10 )
>>{
>> N result = N( );
>>
>> while( *p )
>> {
>> result = result * base + ( *p <= '9' ? *p - '0' : *p - 'a' + 10 );
>> ++p;
>> }
>>
>> return result;
>>}
>>[/color]
>
> You are asuming the ASCII character set? In EBCDIC '9' > 'a'.
>
> Bye
>
> Norbert
>
>[/color]

No assumption, just a mistake. That should have said:

'0' <= *p && *p <= '9'

atoi()

atoi()

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