DOCERR: Online Help Solution for C4139 Warning Is Incorrect

 Last reviewed: July 17, 1997
Article ID: Q64640
6.00 6.00a 6.00ax 7.00 | 6.00 6.00a | 1.00 
MS-DOS                 | OS/2       | WINDOWS
kbtool kbdocerr

The information in this article applies to:

  • The Microsoft C/C++ Compiler (CL.EXE), included with: 

        - Microsoft C for MS-DOS, versions 6.0, 6.0a, and 6.0ax
    - Microsoft C for OS/2, versions 6.0 and 6.0a
    - Microsoft C/C++ for MS-DOS, versions 7.0
    - Microsoft Visual C++ for Windows, version 1.0

SYMPTOMS

Using hexadecimal constants in strings results in the following compiler warning 

   C4139: '0xsequence' : hex escape sequence is out of range
if the hexadecimal digits following the "\x" escape character evaluate to a number too large to be converted to an ASCII character.

The online help systems for Microsoft C versions 6.0, 6.0a, and 6.0ax, and QuickC versions 2.5 and 2.51, show an example of code that produces the following warning: 

   printf("\x7bell\n");   /* Error-causing code */
Next, the following workaround is given to resolve the problem: 

   printf("\x007bell\n");  /* Supposed to resolve problem */
Unfortunately, the second printf statement produces the same error as the first.

With C versions 6.0 and later, the first printf generates the error: 

   C2022: '1982' : too big for character
The online help for C version 8.0 for MS-DOS provides a correct workaround. However, it incorrectly references the octal digits in the workaround as hexadecimal digits. The online help for Visual C++ 1.5 and Visual C++ 1.0 provide the correct information.

CAUSE

The compiler treats every potential hexadecimal digit following the "\x" as part of the constant. This means that "\x007bell" is interpreted as a 5-digit hexadecimal value followed by "ll". Because "\x007be" equals 1982 decimal, a C2022 error will be generated because this value is too large for an ASCII character.

RESOLUTION

Three valid workarounds are listed below:

  • printf("\x007""bell\n"); 

         or
    printf("\0x007bell\n");
  • char TypeArray[] = "\x007""bell";

    printf("%s\n", TypeArray);

    Note: According to the ANSI standard, adjacent string literals are concatenated after escape sequences have been calculated.

  • printf("\007bell\n"); /* Use Octal */

    Note: This workaround uses an octal constant rather than a hexadecimal constant, and is a good solution if portability is a concern. Also note that the documentation for C/C++ version 7.0 and Visual C++ give this as the correct workaround, but call it a 3-digit hexadecimal value rather than a 3-digit octal value.

REFERENCES

Additional information is given in the C 6.0 README.DOC file in Part 2: "Differences between C 5.1 and 6.0," under the subtitle "Hexadecimal Constants in Strings."

Additional reference words: 1.00 6.00 6.00a 6.00ax 7.00 8.00
KBCategory: kbprg kbdocerr
KBSubcategory: CLIss
Keywords : kb16bitonly

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Last reviewed: July 17, 1997
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