HOWTO: Convert a String to a Floating-Point Number

• Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax
• Microsoft C for OS/2, versions 6.0, 6.0a
• Microsoft C/C++ for MS-DOS, version 7.0
• Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.51, 1.52
• Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 5.0, 6.0

SUMMARY

In an application developed with Microsoft C or C/C++, the sscanf() function is a good alternative to the atof() function to convert a string of digits into a floating-point number. If a string does not represent a valid number, atof() returns the value zero; sscanf() returns more useful error information. The application can use the error value from sscanf() with the matherr() function to perform error handling. The atof() function does not call matherr() unless an actual math exception occurs.

The text below presents two recommended methods to convert a string to a floating-point number.

• Validate the string to convert prior to calling the atof() function. Make sure that the string does not contain any non- numeric characters and that the decimal point and sign characters are in the correct locations.



• Use the sscanf() function. It is slower than the atof() function, but it provides better information when an error occurs.

Additional query words:

Keywords          : kbVC100 kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600 
Version           : MS-DOS:6.0,6.00a,6.00ax,7.0; WINDOWS:1.0,1.5,1.51,1.52; WINDOWS NT:1.0,2.0,2.1,4.0,5.0
Platform          : MS-DOS NT WINDOWS 
Issue type        : kbhowto 

Last Reviewed: June 17, 1999