how do I do that using stl

[avi123]

Hello,

I waas wondering how do I do this using std::string instead of char*
sprintf(szStr, "%.2f", dNum);

thanks

[Kheun]

std::string doesn't support such functionalities, use std::stringstream instead.

[avi123]

can you explain me about std::stringstream?
how do I do sprintf with it?
Does it have a function that return std::string?

thanks

[Joe Nellis]

std::string has a member function called c_str() which returns a char*.
sprintf(szStr.c_str(), "%.2f", dNum);

see if that works.

[souldog]

Hi, take a look at the following templates. I believe this
is covered in the FAQ as well

//here are a template functions for converting between numbers to std::string.
//the second parameter should be std::hex, std::oct or std::dec
template <typename T>
std::string convert_to_string(T t, std::ios_base & (*f)(std::ios_base&), const  std::streamsize precision)
{
    std::ostringstream oss;
    oss <<std::fixed<<std::setprecision(precision)<< f << t;
    return oss.str();
};

//from std::string to a number
template <typename T>
bool convert_from_string(T &t, const std::string &s, std::ios_base & (*f)(std::ios_base&), const  std::streamsize precision)
{
    std::istringstream iss(s);
    return !(iss>>f>>std::setprecision(precision)>>std::fixed>>t).fail();
}; 

So your example is implemented as
YourString = convert_to_string(dNum, std::dec, 2);

[souldog]

Oh, by the way, what Joe has suggested here is a very bad
idea. The return value of std::string::c_str() is owned by the
std::string object and should not be modified, nor deleted etc..
If you do then you will find that you have a very unhappy
std::string on your hands.

[Kheun]

Good point, souldog. That's because the memory of std::string is self-managed. If the memory of std::string is being directly manipulated, its state is most likely be corrupted.

By the way, I have find this similar thread which Andreas explained its usage.

[Graham]

... and, of course, std::string::c_str() returns a const char *, so you can't pass it to sprintf, anyway.

[souldog]

sprintf(const_cast<char*>(szStr.c_str()), "%.2f", dNum);

Oh the horror

[Graham]

souldog: please don't use language like that, there may children reading this.

[avi123]

what is stringstream

I found it diffcult to find info about it?
what is it purpose

thanks

[Kheun]

It is stream type that self-manages its memory. By using stringstream, you are equivalent to using sprintf-favour functions and manually managing your memory allocation and deallocation.

You can find information about STL from MSDN.

[avi123]

Originally posted by souldog
Hi, take a look at the following templates. I believe this
is covered in the FAQ as well

//here are a template functions for converting between numbers to std::string.
//the second parameter should be std::hex, std::oct or std::dec
template <typename T>
std::string convert_to_string(T t, std::ios_base & (*f)(std::ios_base&), const  std::streamsize precision)
{
    std::ostringstream oss;
    oss <<std::fixed<<std::setprecision(precision)<< f << t;
    return oss.str();
};

//from std::string to a number
template <typename T>
bool convert_from_string(T &t, const std::string &s, std::ios_base & (*f)(std::ios_base&), const  std::streamsize precision)
{
    std::istringstream iss(s);
    return !(iss>>f>>std::setprecision(precision)>>std::fixed>>t).fail();
}; 

So your example is implemented as
YourString = convert_to_string(dNum, std::dec, 2);

if my dNum = -0.0001
YourString will be "-0.00"
and I need it to be "0.00"

any idea for a simple solution

Thanks