Microsoft KB Archive/11558

= How to convert a string to a floating-point number in C++ =

Article ID: 11558

Article Last Modified on 12/9/2005

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APPLIES TO


 * Microsoft C Professional Development System 6.0a
 * Microsoft C Professional Development System 6.0a
 * Microsoft Visual C++ 1.0 Professional Edition
 * Microsoft Visual C++ 1.5 Professional Edition
 * Microsoft Visual C++ 1.51
 * Microsoft Visual C++ 1.52 Professional Edition
 * Microsoft Visual C++ 2.0 Professional Edition
 * Microsoft Visual C++ 2.1
 * Microsoft Visual C++ 4.0 Standard Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 6.0 Enterprise Edition
 * Microsoft Visual C++ 5.0 Professional Edition
 * Microsoft Visual C++ 6.0 Professional Edition
 * Microsoft Visual C++ 6.0 Standard Edition
 * Microsoft Visual C++ .NET 2002 Standard Edition
 * Microsoft Visual C++ .NET 2003 Standard Edition
 * Microsoft Visual C++ 2005 Express Edition

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This article was previously published under Q11558



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.

Keywords: kbhowtomaster KB11558

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