How to Convert Floating Point Number to String in DLL

The information in this article applies to:

• The C Run-time (CRT), included with: Microsoft Visual C++ for Windows, versions 1.0 and 1.5

SUMMARY

You may want to convert a floating point number to a string in a dynamic link library (DLL) built with Microsoft Visual C++ version 1.0. The functions available to handle float-to-string conversion in a DLL are the C run-time functions _ecvt() and _fcvt(), and will work correctly in code built with all memory models.

MORE INFORMATION

The sample code below demonstrates how to use _ecvt() and _fcvt() to convert a float to a string. These two functions work almost identically. The only difference is that the count parameter for _ecvt() specifies the number of digits to convert in the entire number (both the whole and fractional parts of the number), whereas the count parameter of the _fcvt() function specifies the number of digits after the decimal place (not including the whole part of the number.)

The functions _gcvt() and sprintf() are not available in the run-time libraries for a DLL.

Sample Code

/* Compile options needed:

*/

#include <windows.h>
#include <stdlib.h>

 char *buffer;
 LPSTR startbuffptr;
 static int dec,sign;  // must use static, don't assume SS==DS
 int i;

 startbuffptr = buff;

 buffer = fcvt((double)r,prec,&dec,&sign);
 // buffer = ecvt((double)r,prec,&dec,&sign);

// copy the negative sign if less than zero
 if (sign)
    *buff++ = '-';

// copy the non-fractional part before the decimal place
 for(i=0; i<dec; i++)
    *buff++ = *buffer++;

 *buff++ = '.';  // copy the decimal point into the string
 *buff = '\0';   // don't assume NULL termination

// copy the fractional part after the decimal place
 lstrcat(buff,buffer);

 return startbuffptr;

Module Definition File (.DEF)

LIBRARY FLOAT DESCRIPTION 'FLOAT.DLL -- a dll using ecvt() and fcvt()' EXETYPE WINDOWS

STUB 'WINSTUB.EXE'

CODE PRELOAD MOVEABLE NONDISCARDABLE DATA PRELOAD MOVEABLE SINGLE

HEAPSIZE 1024

EXPORTS

    WEP @1 RESIDENTNAME
    _FloatToString @2