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Converting string to integer

P: n/a
Gil
I have a string :

string A = "2";

I need to get it's integer value :

// ??
int val = A ; // ??
Jul 22 '05 #1
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13 Replies


P: n/a
> I have a string :

string A = "2";

I need to get it's integer value :

// ??
int val = A ; // ??

assuming you include stdlib.h and the string-class provides the
cast-operator to const char*:

int val = atoi(string);

Jul 22 '05 #2

P: n/a

"Gil" <br**************@hotmail.com> wrote in message
news:ad*************************@posting.google.co m...
I have a string :

string A = "2";

I need to get it's integer value :


Check http://www.groups.google.com

Anyways,
int main()
{
string str = "123";
istringstream iss(str);
int x;
iss >> x;
if(iss)
{
// conversion successful
}
else
{
// could not convert str to an int
}
}

Best wishes,
Sharad
Jul 22 '05 #3

P: n/a

"Patrik Stellmann" <st*******@tu-harburg.de> wrote in message
news:bv************@uni-berlin.de...
I have a string :

string A = "2";

I need to get it's integer value :

// ??
int val = A ; // ?? assuming you include stdlib.h and the string-class provides the
cast-operator to const char*:


Sorry, but both of these assumptions are incorrect. The standard header to
include is <cstdlib> nowadays. Furthermore the string class does not provide
an implicit const char* conversion but rather the c_str() member function.

int val = atoi(string);


int val = atoi( A.c_str() );

should do the trick.

Regards
Chris
Jul 22 '05 #4

P: n/a

"Gil" <br**************@hotmail.com> skrev i en meddelelse
news:ad*************************@posting.google.co m...
I have a string :

string A = "2";

I need to get it's integer value :

// ??
int val = A ; // ??


Do yourself two favours:

1) Get the FAQ for this newsgroup and read it all... it is well worth the
effort. The faq can be found at http://www.parashift.com/c++-faq-lite/.

2) Get the boost-library (http://www.boost.org) and look at all the
wonderful things it has to offer - among them the solution to your problem.

Kind regards
Peter
Jul 22 '05 #5

P: n/a
br**************@hotmail.com (Gil) wrote in message news:<ad*************************@posting.google.c om>...
I have a string :

string A = "2";

I need to get it's integer value :

// ??
int val = A ; // ??


hallo

i think you can do so which the function atoi.

int val = atoi(A);

Armando
Jul 22 '05 #6

P: n/a
> > > I have a string :

string A = "2";

I need to get it's integer value :

// ??
int val = A ; // ?? assuming you include stdlib.h and the string-class provides the
cast-operator to const char*:


Sorry, but both of these assumptions are incorrect. The standard header to
include is <cstdlib> nowadays. Furthermore the string class does not provide
an implicit const char* conversion but rather the c_str() member function.


He didn't mention any details about his string class. Maybe you are
confusing it with std::string ?
int val = atoi( A.c_str() );


int val = std::atoi( A.c_str() );

nowadays.
Jul 22 '05 #7

P: n/a
On Wed, 28 Jan 2004 09:32:08 +0100, "Chris Theis"
<Ch*************@nospam.cern.ch> wrote in comp.lang.c++:

"Patrik Stellmann" <st*******@tu-harburg.de> wrote in message
news:bv************@uni-berlin.de...
I have a string :

string A = "2";

I need to get it's integer value :

// ??
int val = A ; // ??

assuming you include stdlib.h and the string-class provides the
cast-operator to const char*:


Sorry, but both of these assumptions are incorrect. The standard header to
include is <cstdlib> nowadays. Furthermore the string class does not provide
an implicit const char* conversion but rather the c_str() member function.

int val = atoi(string);


int val = atoi( A.c_str() );

should do the trick.


No, not really. The ato... functions from the C library should never
be used unless you have already checked the character array and know
that it will not result in a numeric value outside the range of the
given type, in which case you might as well do the conversion yourself
while you are walking the string.

All of the ato... functions generate undefined behavior if the text
string represents a numerical value outside the range of the type.

That is exactly why the strto... functions were added during C
standardization. They have defined behavior for all inputs, other
than being passed a null pointer.

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.learn.c-c++
http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html
Jul 22 '05 #8

P: n/a

"Old Wolf" <ol*****@inspire.net.nz> wrote in message
news:84**************************@posting.google.c om...
> I have a string :
>
> string A = "2";
>
[SNIP]
He didn't mention any details about his string class. Maybe you are
confusing it with std::string ?
The OP declared his string using a class named "string". Without any further
specification it is valid (at least IMHO) to presume that the standard
string class is meant. Anyway, naming your own string class like the
standard one is certainly not the cleverest idea, don't you think?

int val = std::atoi( A.c_str() );

nowadays.


Only if no using namespace statement has been issued, which cannot be
verified from the code snippet.

Chris
Jul 22 '05 #9

P: n/a

"Jack Klein" <ja*******@spamcop.net> wrote in message
news:70********************************@4ax.com...
On Wed, 28 Jan 2004 09:32:08 +0100, "Chris Theis"
<Ch*************@nospam.cern.ch> wrote in comp.lang.c++:
[SNIP]
No, not really. The ato... functions from the C library should never
be used unless you have already checked the character array and know
that it will not result in a numeric value outside the range of the
given type, in which case you might as well do the conversion yourself
while you are walking the string.

All of the ato... functions generate undefined behavior if the text
string represents a numerical value outside the range of the type.

That is exactly why the strto... functions were added during C
standardization. They have defined behavior for all inputs, other
than being passed a null pointer.


I didn't know that ato... might result in undefined behavior. Thanks for
telling me, Jack. However, in C++ I would recommend to use stringstreams
anyway.

Cheers
Chris
Jul 22 '05 #10

P: n/a
Chris Theis wrote:
The OP declared his string using a class named "string". Without any further
specification it is valid (at least IMHO) to presume that the standard
string class is meant. Anyway, naming your own string class like the
standard one is certainly not the cleverest idea, don't you think?

I don't even think it's a legal identifier. I believe that in C++, like
C, all identifiers beginning with "str" and followed by a letter are
reserved.


Brian Rodenborn
Jul 22 '05 #11

P: n/a
Default User wrote:
Chris Theis wrote:
[redacted] I don't even think it's a legal identifier. I believe that in C++, like
C, all identifiers beginning with "str" and followed by a letter are
reserved.


Say what??????????????? Can you quote chapter and verse from the Holy
Standard (or the Holy C standard) on that one?

That would break any code that uses "strange", "strong", "stretch",
etc.. as variables.

Jul 22 '05 #12

P: n/a

"red floyd" <no*****@here.dude> wrote in message news:%7*******************@newssvr25.news.prodigy. com...
Default User wrote:
Chris Theis wrote:

[redacted]
I don't even think it's a legal identifier. I believe that in C++, like
C, all identifiers beginning with "str" and followed by a letter are
reserved.


Say what??????????????? Can you quote chapter and verse from the Holy
Standard (or the Holy C standard) on that one?

He's not quite got it right. The C standard reserves external symbols that
start with str followed by a lower case letter for future use.

You can use them internal to a function or class (or other internal linkage) or
in a namespace other than std or the global namespace.

Jul 22 '05 #13

P: n/a
Ron Natalie wrote:
He's not quite got it right. The C standard reserves external symbols that
start with str followed by a lower case letter for future use.
Yes, I forgot to mention the lowercase part.
You can use them internal to a function or class (or other internal linkage) or
in a namespace other than std or the global namespace.


As far as one could tell from example, it was in the global namespace.

Brian Rodenborn
Jul 22 '05 #14

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