What's the equivalent of cout for output to strings?
I should know this already but..开发者_JAVA技巧. printf
is to sprintf
as cout
is to ____
? Please give an example.
It sounds like you are looking for std::ostringstream
.
Of course C++ streams don't use format-specifiers like C's printf()
-type functions; they use manipulators
.
Example, as requested:
#include <sstream>
#include <iomanip>
#include <cassert>
std::string stringify(double x, size_t precision)
{
std::ostringstream o;
o << std::fixed << std::setprecision(precision) << x;
return o.str();
}
int main()
{
assert(stringify(42.0, 6) == "42.000000");
return 0;
}
#include <iostream>
#include <sstream>
using namespace std;
int main()
{
ostringstream s;
s.precision(3);
s << "pi = " << fixed << 3.141592;
cout << s.str() << endl;
return 0;
}
Output:
pi = 3.142
Here's an example:
#include <sstream>
int main()
{
std::stringstream sout;
sout << "Hello " << 10 << "\n";
const std::string s = sout.str();
std::cout << s;
return 0;
}
If you want to clear the stream for reuse, you can do
sout.str(std::string());
Also look at the Boost Format library.
std::ostringstream
You can use this to create something like the Boost lexical cast:
#include <sstream>
#include <string>
template <typename T>
std::string ToString( const T & t ) {
std::ostringstream os;
os << t;
return os.str();
}
In use:
string is = ToString( 42 ); // is contains "42"
string fs = ToString( 1.23 ) ; // fs contains something approximating "1.23"
You have a little misunderstanding for the concept of cout. cout is a stream and the operator << is defined for any stream. So, you just need another stream that writes to string in order to output your data. You can use a standard stream like std::ostringstream or define your own one.
So your analogy is not very precise, since cout is not a function like printf and sprintf
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