INFO: toupper() Generates C4135 or C4244 Warning

Last reviewed: September 4, 1997
Article ID: Q65306

The information in this article applies to:

The C Run-time, included with: - Microsoft C for MS-DOS, versions 6.0, 6.0a, 6.0ax - Microsoft C/C++ for MS-DOS, version 7.0 - Microsoft Visual C++ for Windows, versions 1.0, 1.5 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 2.1, 4.0, 5.0

When compiling a function that contains a call to toupper() in the following format:

   char toupper (char)

at warning level 4, the compiler will generate the following warning message:

   C4135: Conversion between two integral types

With Visual C++ version 4.0, the compiler will generate the following warning message:

   warning C4244: '<operator>' : conversion from 'int ' to 'char ',
   possible loss of data

Because the ANSI-standard draft of December 7, 1988, specifies the syntax for this function as follows, the warning is in compliance with the standard:

   int toupper (int)

The error can be resolved by casting the return value. For example:

   char a, b;
     a = (char)toupper(b);

Keywords          : CRTIss kberrmsg kbfasttip
Version           : MS-DOS:6.0,6.00a,6.00ax,7.0; WINDOWS:1.0,1.5; WINDOWS  NT:1.0,2.0,2.1,4.0,5.0
Platform          : MS-DOS NT WINDOWS
Issue type        : kbinfo

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Last reviewed: September 4, 1997
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