INFO: toupper() Generates C4135 or C4244 Warning

ID: Q65306

The information in this article applies to:

The C Run-time,
- 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, 16-bit edition, versions 1.0, 1.5
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 5.0, 6.0

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);

Additional query words:


Keywords          : kberrmsg kbCRT kbVC100 kbVC150 kbVC200 kbVC210 kbVC400 kbVC500 kbVC600 
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

Last Reviewed: June 30, 1999