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This question already has answers here:
Easiest way to convert int to string in C++
(30 answers)
Closed 7 years ago.
I was wondering if there was an alternative to itoa() for converting an integer to a string because when I run it in visual Studio I get warnings, and when I try to build my program under Linux, I get a compilation error.
In C++11 you can use std::to_string:
#include <string>
std::string s = std::to_string(5);
If you're working with prior to C++11, you could use C++ streams:
#include <sstream>
int i = 5;
std::string s;
std::stringstream out;
out << i;
s = out.str();
Taken from http://notfaq.wordpress.com/2006/08/30/c-convert-int-to-string/
boost::lexical_cast works pretty well.
#include <boost/lexical_cast.hpp>
int main(int argc, char** argv) {
std::string foo = boost::lexical_cast<std::string>(argc);
}
Archeology
itoa was a non-standard helper function designed to complement the atoi standard function, and probably hiding a sprintf (Most its features can be implemented in terms of sprintf): http://www.cplusplus.com/reference/clibrary/cstdlib/itoa.html
The C Way
Use sprintf. Or snprintf. Or whatever tool you find.
Despite the fact some functions are not in the standard, as rightly mentioned by "onebyone" in one of his comments, most compiler will offer you an alternative (e.g. Visual C++ has its own _snprintf you can typedef to snprintf if you need it).
The C++ way.
Use the C++ streams (in the current case std::stringstream (or even the deprecated std::strstream, as proposed by Herb Sutter in one of his books, because it's somewhat faster).
Conclusion
You're in C++, which means that you can choose the way you want it:
The faster way (i.e. the C way), but you should be sure the code is a bottleneck in your application (premature optimizations are evil, etc.) and that your code is safely encapsulated to avoid risking buffer overruns.
The safer way (i.e., the C++ way), if you know this part of the code is not critical, so better be sure this part of the code won't break at random moments because someone mistook a size or a pointer (which happens in real life, like... yesterday, on my computer, because someone thought it "cool" to use the faster way without really needing it).
Try sprintf():
char str[12];
int num = 3;
sprintf(str, "%d", num); // str now contains "3"
sprintf() is like printf() but outputs to a string.
Also, as Parappa mentioned in the comments, you might want to use snprintf() to stop a buffer overflow from occuring (where the number you're converting doesn't fit the size of your string.) It works like this:
snprintf(str, sizeof(str), "%d", num);
Behind the scenes, lexical_cast does this:
std::stringstream str;
str << myint;
std::string result;
str >> result;
If you don't want to "drag in" boost for this, then using the above is a good solution.
We can define our own iota function in c++ as:
string itoa(int a)
{
string ss=""; //create empty string
while(a)
{
int x=a%10;
a/=10;
char i='0';
i=i+x;
ss=i+ss; //append new character at the front of the string!
}
return ss;
}
Don't forget to #include <string>.
С++11 finally resolves this providing std::to_string.
Also boost::lexical_cast is handy tool for older compilers.
I use these templates
template <typename T> string toStr(T tmp)
{
ostringstream out;
out << tmp;
return out.str();
}
template <typename T> T strTo(string tmp)
{
T output;
istringstream in(tmp);
in >> output;
return output;
}
Try Boost.Format or FastFormat, both high-quality C++ libraries:
int i = 10;
std::string result;
WIth Boost.Format
result = str(boost::format("%1%", i));
or FastFormat
fastformat::fmt(result, "{0}", i);
fastformat::write(result, i);
Obviously they both do a lot more than a simple conversion of a single integer
You can actually convert anything to a string with one cleverly written template function. This code example uses a loop to create subdirectories in a Win-32 system. The string concatenation operator, operator+, is used to concatenate a root with a suffix to generate directory names. The suffix is created by converting the loop control variable, i, to a C++ string, using the template function, and concatenating that with another string.
//Mark Renslow, Globe University, Minnesota School of Business, Utah Career College
//C++ instructor and Network Dean of Information Technology
#include <cstdlib>
#include <iostream>
#include <string>
#include <sstream> // string stream
#include <direct.h>
using namespace std;
string intToString(int x)
{
/**************************************/
/* This function is similar to itoa() */
/* "integer to alpha", a non-standard */
/* C language function. It takes an */
/* integer as input and as output, */
/* returns a C++ string. */
/* itoa() returned a C-string (null- */
/* terminated) */
/* This function is not needed because*/
/* the following template function */
/* does it all */
/**************************************/
string r;
stringstream s;
s << x;
r = s.str();
return r;
}
template <class T>
string toString( T argument)
{
/**************************************/
/* This template shows the power of */
/* C++ templates. This function will */
/* convert anything to a string! */
/* Precondition: */
/* operator<< is defined for type T */
/**************************************/
string r;
stringstream s;
s << argument;
r = s.str();
return r;
}
int main( )
{
string s;
cout << "What directory would you like me to make?";
cin >> s;
try
{
mkdir(s.c_str());
}
catch (exception& e)
{
cerr << e.what( ) << endl;
}
chdir(s.c_str());
//Using a loop and string concatenation to make several sub-directories
for(int i = 0; i < 10; i++)
{
s = "Dir_";
s = s + toString(i);
mkdir(s.c_str());
}
system("PAUSE");
return EXIT_SUCCESS;
}
Allocate a string of sufficient length, then use snprintf.
int number = 123;
stringstream = s;
s << number;
cout << ss.str() << endl;
I wrote this thread-safe function some time ago, and am very happy with the results and feel the algorithm is lightweight and lean, with performance that is about 3X the standard MSVC _itoa() function.
Here's the link. Optimal Base-10 only itoa() function? Performance is at least 10X that of sprintf(). The benchmark is also the function's QA test, as follows.
start = clock();
for (int i = LONG_MIN; i < LONG_MAX; i++) {
if (i != atoi(_i32toa(buff, (int32_t)i))) {
printf("\nError for %i", i);
}
if (!i) printf("\nAt zero");
}
printf("\nElapsed time was %f milliseconds", (double)clock() - (double)(start));
There are some silly suggestions made about using the caller's storage that would leave the result floating somewhere in a buffer in the caller's address space. Ignore them. The code I listed works perfectly, as the benchmark/QA code demonstrates.
I believe this code is lean enough to use in an embedded environment. YMMV, of course.
The best answer, IMO, is the function provided here:
http://www.jb.man.ac.uk/~slowe/cpp/itoa.html
It mimics the non-ANSI function provided by many libs.
char* itoa(int value, char* result, int base);
It's also lightning fast and optimizes well under -O3, and the reason you're not using c++ string_format() ... or sprintf is that they are too slow, right?
If you are interested in fast as well as safe integer to string conversion method and not limited to the standard library, I can recommend the format_int method from the {fmt} library:
fmt::format_int(42).str(); // convert to std::string
fmt::format_int(42).c_str(); // convert and get as a C string
// (mind the lifetime, same as std::string::c_str())
According to the integer to string conversion benchmarks from Boost Karma, this method several times faster than glibc's sprintf or std::stringstream. It is even faster than Boost Karma's own int_generator as was confirm by an independent benchmark.
Disclaimer: I'm the author of this library.
Note that all of the stringstream methods may involve locking around the use of the locale object for formatting. This may be something to be wary of if you're using this conversion from multiple threads...
See here for more. Convert a number to a string with specified length in C++
On Windows CE derived platforms, there are no iostreams by default. The way to go there is preferaby with the _itoa<> family, usually _itow<> (since most string stuff are Unicode there anyway).
Most of the above suggestions technically aren't C++, they're C solutions.
Look into the use of std::stringstream.
is there any alternative to atof, strtod, lexical_cast, stringstream or sprintf?
that is:
fast
C++ way (std::string instead of char*)
safe (no buffer overrun risk)
valid (return NaN if conversion couldn't be made)
no external library (independent)
I prefer more like this , a simple function, optimized, and to the point
reason :
atof and strtod is C function and they are not returning NaN upon failure, I prefer working on std::string, so I just asking if anyone already writing some wrapper to std::string that I can use (if you don't mind).
lexical_cast has boost dependency
stringstream is slow
sprintf has buffer overflow risk and its C function
I'd look at Boost Spirit
http://www.boost.org/doc/libs/1_47_0/libs/spirit/doc/html/spirit/qi/reference/numeric/real.html
At least the benchmarks of the formatters (that is float -> string) consistently turn out as top-of-the-bill*1*
Also the exact input format specification and semantics when parsing can be configured very nicely using a policy class.
Here is my absolute min-dependency use of qi::any_real_parser<> and the list of dependendencies it touches:
#include <boost/spirit/include/qi_real.hpp>
namespace qi = boost::spirit::qi;
int main()
{
const char input[] = "3.1415926";
const char *f(input);
const char *l(f+strlen(input));
qi::any_real_parser<double> x;
double parsed;
x.parse(f, l, qi::unused, qi::unused, parsed);
return 0;
}
boost/concept
boost/config
boost/detail
boost/exception
boost/fusion
boost/iterator
boost/math
boost/mpl
boost/optional
boost/preprocessor
boost/proto
boost/range
boost/regex
boost/spirit
boost/typeof
boost/type_traits
boost/utility
boost/variant
aligned_storage.hpp,assert.hpp,blank_fwd.hpp,blank.hpp,call_traits.hpp,checked_delete.hpp,concept_check.hpp,config.hpp,cstdint.hpp,current_function.hpp,foreach_fwd.hpp,foreach.hpp,get_pointer.hpp,implicit_cast.hpp,iterator.hpp,limits.hpp,math_fwd.hpp,next_prior.hpp,noncopyable.hpp,none.hpp,none_t.hpp,optional.hpp,ref.hpp,static_assert.hpp,swap.hpp,throw_exception.hpp,type.hpp,utility.hpp,variant.hpp,version.hpp
1 e.g. http://www.boost.org/doc/libs/1_47_0/libs/spirit/doc/html/spirit/karma/performance_measurements/numeric_performance/double_performance.html
If you want to convert from numerical types to std::string there's a std::to_string function available in the latest standard.
Unfortunately as I've found out recently, in Visual Studio 2010 it is somewhat limited because there are only three overloads available for it; long double, long long, and unsigned long long. This causes issues when trying to use them from within templates.
The fast format library should be able to do the kinds of transformations you're looking for, at least for writing a float out. It does not handle parsing of a float, however.
So recently I got into a debate about how to solve a problem, the problem specifically was: How do I find all the pallindromes between 1 and 1 million. I said, "Use atoi to make a string, use a for loop to reverse the string, the use strcmp to compare the string(s) in question.
A few minutes later someone asked "Why would you use a C-style solution in C++." I found myself confused of a simple, more "C++" way of solving this with code as direct and easy to understand. Anyone care to illuminate me on this one?
edit: itoa not atoi
Quite simply, C++ streams are guaranteed to be memory safe and exception safe, failure is distinct from any return value, and C++ strings are memory-safe and exception-safe. C-strings and atoi are hideously unsafe in pretty much every way known to man. Code written in that way is much more error-prone.
Example C++ solution:
#include <algorithm>
#include <iterator>
#include <iostream>
#include <boost/iterator/counting_iterator.hpp>
#include <boost/lexical_cast.hpp>
namespace {
bool is_palindrome(unsigned int i) {
const std::string& s = boost::lexical_cast<std::string>(i);
return std::equal(s.begin(), s.end(), s.rbegin());
}
const unsigned int stop = 1000000;
}
int main() {
std::remove_copy_if(boost::counting_iterator<unsigned int>(1),
boost::counting_iterator<unsigned int>(stop),
std::ostream_iterator<unsigned int>(std::cout, "\n"),
std::not1(std::ptr_fun(is_palindrome)));
}
(I used std::remove_copy_if to make up for the lack of std::copy_if which is in C++0x)
For completeness sake I implemented a version that generates the palindromes rather than testing candidates against a predicate:
#include <boost/lexical_cast.hpp>
#include <boost/iterator/counting_iterator.hpp>
#include <boost/iterator/transform_iterator.hpp>
#include <algorithm>
#include <iterator>
#include <iostream>
#include <cassert>
namespace {
template <int ver>
unsigned int make_palindrome(unsigned int i) {
std::string s = boost::lexical_cast<std::string>(i);
assert(s.size());
s.reserve(s.size()*2);
std::reverse_copy(s.begin(), s.end()-ver, std::back_inserter(s));
return boost::lexical_cast<unsigned int>(s);
}
}
int main() {
typedef boost::counting_iterator<unsigned int> counter;
std::merge(boost::make_transform_iterator(counter(1), make_palindrome<1>),
boost::make_transform_iterator(counter(999), make_palindrome<1>),
boost::make_transform_iterator(counter(1), make_palindrome<0>),
boost::make_transform_iterator(counter(999), make_palindrome<0>),
std::ostream_iterator<unsigned int>(std::cout, "\n"));
}
(I could have used boost.range I think instead of std::merge for this)
The discussion point from this I guess then is "is this a better* way to write it?". The thing I like about writing problems like the palindrome in this style is you get the "if it compiles it's probably correct" heuristic on your side. Even if there is a bug it'll still get handled sensibly at run time (e.g. an exception from lexical_cast).
It's a markedly different way of thinking from C programming (but strangely similar to Haskell in some ways). It brings benefits in the form of lots of extra safety, but the compiler error messages can be terrible and shifting the way you think about problems is hard.
At the end of it all though what matters is "is it less work for less bugs?". I can't answer that without some metrics to help.
* For some definition of better.
The C++ equivalent to your solution would be to:
Use stringstream to turn the number into a std::string.
Use std::reverse_copy to reverse the string.
Use == to compare the strings.
1 is better than using itoa (which you probably meant) because you don't have to allocate the memory for the created string yourself and there's no chance of a buffer overrun.
2 is better because again you don't have to worry about allocating memory for the reversed string and you don't duplicate existing functionality.
3 is better because string1 == string2 reads better than using strcmp.
atoi makes it impossible to detect input errors. While a stringstream can do the same job and can errors can be easily detected.
I think a more appropriate question would be why shouldn't you use C-based solutions in C++? If it is simpler and more readable than a "pure" C++ solution, I know I would opt for the C-style solution. Given the solution you came up with was clever and simple, a corresponding C++ solution may be overkill and given the simplicity of the problem I'm not sure what was being suggested that C++ can bring to the solution.
What is the most optimal way to achieve the same as this?
void foo(double floatValue, char* stringResult)
{
sprintf(stringResult, "%f", floatValue);
}
I'm sure someone will say boost::lexical_cast, so go for that if you're using boost, but it's basically the same as this anyway:
#include <sstream>
#include <string>
std::string doubleToString(double d)
{
std::ostringstream ss;
ss << d;
return ss.str();
}
Note that you could easily make this into a template that works on anything that can be stream-inserted (not just doubles).
http://www.cplusplus.com/reference/iostream/stringstream/
double d=123.456;
stringstream s;
s << d; // insert d into s
Boost::lexical_cast<>
On dinkumware STL, the stringstream is filled out by the C library snprintf.
Thus using snprintf formatting directly will be comparable with the STL formatting part.
But someone once told me that the whole is greater than or equal to the sum of its known parts.
As it will be platform dependent as to whether stringstream will do an allocation (and I am quite sure that DINKUMWARE DOES NOT YET include a small buffer in stringstream for conversions of single items like yours) it is truely doubtful that ANYTHING that requires an allocation (ESPECIALLY if MULTITHREADED) can compete with snprintf.
In fact (formatting+allocation) has a chance of being really terrible as an allocation and a release might well require 2 full read-modify-write cycles in a multithreaded environment unless the allocation implementation has a thread local small heap.
That being said, if I was truely concerned about performance, I would take the advice from some of the other comments above, change the interface to include a size and use snprintf - i.e.
bool
foo(const double d, char* const p, const size_t n){
use snprintf......
determine if it fit, etc etc etc.
}
If you want a std::string you are still better off using the above and instantiating the string from the resultant char* as there will be 2 allocations + 2 releases involved with the std::stringstream, std::string solution.
BTW I cannot tell if the "string" in the question is std::string or just generic ascii chars usage of "string"
The best thing to do would be to build a simple templatized function to convert any streamable type into a string. Here's the way I do it:
#include <sstream>
#include <string>
template <typename T>
const std::string to_string(const T& data)
{
std::ostringstream conv;
conv << data;
return conv.str();
}
If you want a const char* representation, simply substitute conv.str().c_str() in the above.
I'd probably go with what you suggested in your question, since there's no built-in ftoa() function and sprintf gives you control over the format. A google search for "ftoa asm" yields some possibly useful results, but I'm not sure you want to go that far.
I'd say sprintf is pretty much the optimal way. You may prefer snprintf over it, but it doesn't have much to do with performance.
Herb Sutter has done an extensive study on the alternatives for converting an int to a string, but I would think his arguments hold for a double as well.
He looks at the balances between safety, efficiency, code clarity and usability in templates.
Read it here: http://www.gotw.ca/publications/mill19.htm
_gcvt or _gcvt_s.
If you use the Qt4 frame work you could go :
double d = 5.5;
QString num = QString::number(d);
This is very useful thread. I use sprintf_s for it but I started to doubt if it is really faster than other ways. I came across following document on Boost website which shows performance comparison between Printf/scanf, StringStream and Boost.
Double to String is most common conversion we do in our code, so i'll stick with what i've been using. But, using Boost in other scenarios could be your deciding factor.
http://www.boost.org/doc/libs/1_58_0/doc/html/boost_lexical_cast/performance.html
In the future, you can use std::to_chars to write code like https://godbolt.org/z/cEO4Sd . Unfortunately, only VS2017 and VS2019 support part of this functionality...
#include <iostream>
#include <charconv>
#include <system_error>
#include <string_view>
#include <array>
int main()
{
std::array<char, 10> chars;
auto [parsed, error] = std::to_chars(
chars.data(),
chars.data() + chars.size(),
static_cast<double>(12345.234)
);
std::cout << std::string_view(chars.data(), parsed - chars.data());
}
For a lengthy discussion on MSVC details, see
https://www.reddit.com/r/cpp/comments/a2mpaj/how_to_use_the_newest_c_string_conversion/eazo82q/
This question already has answers here:
Easiest way to convert int to string in C++
(30 answers)
Closed 7 years ago.
I was wondering if there was an alternative to itoa() for converting an integer to a string because when I run it in visual Studio I get warnings, and when I try to build my program under Linux, I get a compilation error.
In C++11 you can use std::to_string:
#include <string>
std::string s = std::to_string(5);
If you're working with prior to C++11, you could use C++ streams:
#include <sstream>
int i = 5;
std::string s;
std::stringstream out;
out << i;
s = out.str();
Taken from http://notfaq.wordpress.com/2006/08/30/c-convert-int-to-string/
boost::lexical_cast works pretty well.
#include <boost/lexical_cast.hpp>
int main(int argc, char** argv) {
std::string foo = boost::lexical_cast<std::string>(argc);
}
Archeology
itoa was a non-standard helper function designed to complement the atoi standard function, and probably hiding a sprintf (Most its features can be implemented in terms of sprintf): http://www.cplusplus.com/reference/clibrary/cstdlib/itoa.html
The C Way
Use sprintf. Or snprintf. Or whatever tool you find.
Despite the fact some functions are not in the standard, as rightly mentioned by "onebyone" in one of his comments, most compiler will offer you an alternative (e.g. Visual C++ has its own _snprintf you can typedef to snprintf if you need it).
The C++ way.
Use the C++ streams (in the current case std::stringstream (or even the deprecated std::strstream, as proposed by Herb Sutter in one of his books, because it's somewhat faster).
Conclusion
You're in C++, which means that you can choose the way you want it:
The faster way (i.e. the C way), but you should be sure the code is a bottleneck in your application (premature optimizations are evil, etc.) and that your code is safely encapsulated to avoid risking buffer overruns.
The safer way (i.e., the C++ way), if you know this part of the code is not critical, so better be sure this part of the code won't break at random moments because someone mistook a size or a pointer (which happens in real life, like... yesterday, on my computer, because someone thought it "cool" to use the faster way without really needing it).
Try sprintf():
char str[12];
int num = 3;
sprintf(str, "%d", num); // str now contains "3"
sprintf() is like printf() but outputs to a string.
Also, as Parappa mentioned in the comments, you might want to use snprintf() to stop a buffer overflow from occuring (where the number you're converting doesn't fit the size of your string.) It works like this:
snprintf(str, sizeof(str), "%d", num);
Behind the scenes, lexical_cast does this:
std::stringstream str;
str << myint;
std::string result;
str >> result;
If you don't want to "drag in" boost for this, then using the above is a good solution.
We can define our own iota function in c++ as:
string itoa(int a)
{
string ss=""; //create empty string
while(a)
{
int x=a%10;
a/=10;
char i='0';
i=i+x;
ss=i+ss; //append new character at the front of the string!
}
return ss;
}
Don't forget to #include <string>.
С++11 finally resolves this providing std::to_string.
Also boost::lexical_cast is handy tool for older compilers.
I use these templates
template <typename T> string toStr(T tmp)
{
ostringstream out;
out << tmp;
return out.str();
}
template <typename T> T strTo(string tmp)
{
T output;
istringstream in(tmp);
in >> output;
return output;
}
Try Boost.Format or FastFormat, both high-quality C++ libraries:
int i = 10;
std::string result;
WIth Boost.Format
result = str(boost::format("%1%", i));
or FastFormat
fastformat::fmt(result, "{0}", i);
fastformat::write(result, i);
Obviously they both do a lot more than a simple conversion of a single integer
You can actually convert anything to a string with one cleverly written template function. This code example uses a loop to create subdirectories in a Win-32 system. The string concatenation operator, operator+, is used to concatenate a root with a suffix to generate directory names. The suffix is created by converting the loop control variable, i, to a C++ string, using the template function, and concatenating that with another string.
//Mark Renslow, Globe University, Minnesota School of Business, Utah Career College
//C++ instructor and Network Dean of Information Technology
#include <cstdlib>
#include <iostream>
#include <string>
#include <sstream> // string stream
#include <direct.h>
using namespace std;
string intToString(int x)
{
/**************************************/
/* This function is similar to itoa() */
/* "integer to alpha", a non-standard */
/* C language function. It takes an */
/* integer as input and as output, */
/* returns a C++ string. */
/* itoa() returned a C-string (null- */
/* terminated) */
/* This function is not needed because*/
/* the following template function */
/* does it all */
/**************************************/
string r;
stringstream s;
s << x;
r = s.str();
return r;
}
template <class T>
string toString( T argument)
{
/**************************************/
/* This template shows the power of */
/* C++ templates. This function will */
/* convert anything to a string! */
/* Precondition: */
/* operator<< is defined for type T */
/**************************************/
string r;
stringstream s;
s << argument;
r = s.str();
return r;
}
int main( )
{
string s;
cout << "What directory would you like me to make?";
cin >> s;
try
{
mkdir(s.c_str());
}
catch (exception& e)
{
cerr << e.what( ) << endl;
}
chdir(s.c_str());
//Using a loop and string concatenation to make several sub-directories
for(int i = 0; i < 10; i++)
{
s = "Dir_";
s = s + toString(i);
mkdir(s.c_str());
}
system("PAUSE");
return EXIT_SUCCESS;
}
Allocate a string of sufficient length, then use snprintf.
int number = 123;
stringstream = s;
s << number;
cout << ss.str() << endl;
I wrote this thread-safe function some time ago, and am very happy with the results and feel the algorithm is lightweight and lean, with performance that is about 3X the standard MSVC _itoa() function.
Here's the link. Optimal Base-10 only itoa() function? Performance is at least 10X that of sprintf(). The benchmark is also the function's QA test, as follows.
start = clock();
for (int i = LONG_MIN; i < LONG_MAX; i++) {
if (i != atoi(_i32toa(buff, (int32_t)i))) {
printf("\nError for %i", i);
}
if (!i) printf("\nAt zero");
}
printf("\nElapsed time was %f milliseconds", (double)clock() - (double)(start));
There are some silly suggestions made about using the caller's storage that would leave the result floating somewhere in a buffer in the caller's address space. Ignore them. The code I listed works perfectly, as the benchmark/QA code demonstrates.
I believe this code is lean enough to use in an embedded environment. YMMV, of course.
The best answer, IMO, is the function provided here:
http://www.jb.man.ac.uk/~slowe/cpp/itoa.html
It mimics the non-ANSI function provided by many libs.
char* itoa(int value, char* result, int base);
It's also lightning fast and optimizes well under -O3, and the reason you're not using c++ string_format() ... or sprintf is that they are too slow, right?
If you are interested in fast as well as safe integer to string conversion method and not limited to the standard library, I can recommend the format_int method from the {fmt} library:
fmt::format_int(42).str(); // convert to std::string
fmt::format_int(42).c_str(); // convert and get as a C string
// (mind the lifetime, same as std::string::c_str())
According to the integer to string conversion benchmarks from Boost Karma, this method several times faster than glibc's sprintf or std::stringstream. It is even faster than Boost Karma's own int_generator as was confirm by an independent benchmark.
Disclaimer: I'm the author of this library.
Note that all of the stringstream methods may involve locking around the use of the locale object for formatting. This may be something to be wary of if you're using this conversion from multiple threads...
See here for more. Convert a number to a string with specified length in C++
On Windows CE derived platforms, there are no iostreams by default. The way to go there is preferaby with the _itoa<> family, usually _itow<> (since most string stuff are Unicode there anyway).
Most of the above suggestions technically aren't C++, they're C solutions.
Look into the use of std::stringstream.