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: July 1, 1999
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