[C++] converting a float to a string.

[Clyde]

I've seen on google search allready about sorta doing this but it's using cout ( print to console ) what im really after is converting a float ( my fps calc ) into a string ready for use with a print_bitmap_text routine.

Cheers and many thanks,
from Clyde.
xxxx

[ninogenio]

hey dude check this out,

Code: [Select]

#include <stdio.h>

int main ()
{
  char buffer [50];
  int n, a=5, b=3;
  n=sprintf (buffer, "%d plus %d is %d", a, b, a+b);
  printf ("[%s] is a %d char long string\n",buffer,n);
  return 0;
}

now what this does is use sprintf to convert the ints into a string format to use floats just change the %d to %f and there are a lot of other diffrent switches that can be used you can even format the buffer to contain floats and ints and whatever else.

then instead of using printf just dump the buffer into whatever you use to print.

[edit forgot to say n contains string length but you dont have to assign sprintf to anything if you dont want.]

[ninogenio]

your welcome mate! 

[Clyde]

Thanks Ninogenio, I really appreciate it at the moment I haven't tried this yet looks cool. Im trying to visualize that in draw_text( char *message, x, y );

[Jim]

You can do

Code: [Select]

float a=1.2345f;
char tmp[50];
sprintf(tmp, "%f", a)
draw_text(tmp, x, y);
Your next question is going to be "how do I make it only have 2 decimal places"

Code: [Select]

sprintf(tmp, "%.2f", a)

Jim

[Clyde]

I see so that sprintf is printing / feeding into the string.

[LittleWhite]

If you really want C++ stuff (I mean no sprintf function from the C library), you can use the streamstring (http://www.cplusplus.com/reference/iostream/stringstream/).

If I remember well it will be something like this:

Code: [Select]

std::streamstring ss;
float myFloat = 3.14f; // Pure random float
ss << myFloat;
// And you can get the string like this:
ss.str();
// Or the char* like this:
ss.str().c_str();


[James_wright_1990]

I recenty had the same problem and for some reason my lecturers don't like us using stdio.h(I dont know why) so I also use stringstream the code looks like:

Code: [Select]

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main (int argc, char **argv)
{
float f = 3.33333f;

ostringstream os;
os << f;

string s = os.str();

cout << s << endl;

             int k;
cin >> k; // pauses the program

return 0;
}
This then prints to the console but you dont have to this is just the code I used whilst trying to figure out how to do it. If  you need to limit the decimal points I used this code :

Code: [Select]

#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>

using namespace std;

int main (int argc, char **argv)
{
float f = 3.33333;

ostringstream os;
os << dec << setprecision(4) << f;

string s = os.str();

cout << s << endl;

             int k;
cin >> k; // pauses the program

return 0;
}
Not sure how good this code is as a solution but it seams to be working for me.

James.

[LittleWhite]

Your code is correct.

Just that you don't need to use another variable for the string, to be able to display it.

I mean

Code: [Select]

std::cout << os.str() << std::endl;
Will do the job, without using the string s.
Lecturers can dislike old C functions because they does not launch exceptions, when they are falling, or stuff like this.

[Jim]

sprintf is totally unsafe, as you have no way of making sure the workspace you give it is going to be big enough (the cause of many stack/heap overflow exploitz), that's why I made it 50, but I pulled that number out of my arse.

So there is either the C++ stringstream route or the Safer C library (which is part of Visual Studio 2005 and later) which has sprintf_s() where one of the parameters is the output buffer size.

I think some people also have an aversion to mixing C++ includes and C .h includes, though it's just stylistic and should always be OK - as James shows, all the C functions appear in the std namespace.

Jim

[LittleWhite]

I think the libc ( not VS "crappy" implementation ) has the snprintf (with a n somewhere in the same) where you have to put a size array to avoid all problems ( like the secure version )