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CC Compiler 5.5.0.00077 -- Array Init causing Error #28 for any element that is a "const char * xxxxx = "some string"

Normand Martel77
Prodigy 70 points


The items high-lighted below (7 of them) cause Error #28 -- interestingly, they are the only items that are declared as "const char *"

The non-const items seem fine but the compiler is flagging the const strings with 

"error #28 expression must have a constant value".  All the items in this area are constant items... they are pointers and are all resolved at link time.  The only difference I can see is the ones being complained about will reside in code flash.  The others land in ram, but I think that the address the items land in should be irrelevant.  I've used the same code on IAR and Keil and both of those compilers work fine.

the constant expression "const char *    szCompany     ="MyCompany"; "

is declared as "extern const char * szCompany"  in a header file included by the code below.

the expression "char * szSessionID = "0xxxxx" "

is declared as "extern char * szSessionID"

The const item generates error #28 and the item without const compiles fine.   This seems to be a compiler issue.  Suggestions?

///////////////////////////////////////////////////////////////////////////////
//
// MSP Get Attributes - Attributes Pointer Table
//
///////////////////////////////////////////////////////////////////////////////
const char* MWP_Attributes_Table[ ATTRIBUTE_ENTRY_COUNT ] =
{
  { NULL }, // spare00
  { &SetMyName[SHORT_NAME_OFFSET] }, // ShortName
  { szCompany }, // VendorName
  { szModel }, // VendorModel
  { szFirmwareRev }, // VendorVersion
  { szPlatform }, // PlatformModel
  { &szHwRevNo[13] }, // HardwareRevision 
  { szPlatformRev }, // FirmwareRevision
  { szPlatformDate }, // FirmwareDate
  { &szSerialNo[4] }, // SerialNumber
  { szSessionID }, // SessionId
  { &szPatient[9] }, // PatientId
  { &szDOB[9] }, // PatientDOB
  { szDate }, // SessionDate
  { szTime }, // SessionTime
  { &szOperatingMode[12] }, // SessionType
  { &szRecLength[9] }, // SessionDuration
  { szCableType }, // CableType
  { szLeadText }, // LeadConfiguration
  { &szSampleRate[9] }, // SampleRate
  { &szResolution[11] }, // DataResolution
  { szPackType }, // DataFormat
  { NULL }, // EcgRecordingDuration (Integer in Hours)?
  { NULL }, // spare23
  { NULL }, // spare24
  { NULL }, // spare25
  { NULL }, // spare26
  { NULL }, // spare27
  { NULL }, // spare28
  { NULL }, // spare29
  { NULL }, // spare30
  { NULL } // spare31
};

  • 0
    TI__Guru**** 251300 points

    I can reproduce this diagnostic with the TI MSP430 compiler ...

    Normand Martel77 said:
    "error #28 expression must have a constant value".

    But I cannot reproduce this ...

    Normand Martel77 said:
    I've used the same code on IAR and Keil and both of those compilers work fine.

    I don't have those compilers.  But I do have two different versions of the gcc compiler.  And both of them give a similar error the the TI compiler.

    I'd appreciate if you would submit an example, source code and build options, which builds clean with the gcc compiler, but fails for the TI compiler.

    Thanks and regards,

    -George

  • 0
    TI__Guru* 84285 points
    In C, the expression "szCompany" is not a constant expression. It is a variable. The fact that its value is a pointer is irrelevant.
    If you had declared it like this:
    const char szCompany[] = "MyCompany";
    you could have used the expression "szCompany." In that case, it is a constant expression because when you use the name of an array without a subscript, you get the address of the array, which is a constant expression.
  • 0 in reply to George Mock
    Prodigy 70 points
    Thanks George. I am under time constraints so can't submit anything sanitized right now.
    Another post suggested using the char Value[] form (Even with the const) and that works.
    Since at compile/link time these values resolve, it should have worked.
    I don't mind changing to the array form to get to the finish line, as the code generated works correctly.

    Thanks again.
  • 0 in reply to Normand Martel77
    TI__Guru* 84285 points

    Normand Martel77 said:
    Since at compile/link time these values resolve, it should have worked.

    The expression must be a constant expression at compile time, and the pointer form is not.  This is not a flaw in the compiler, it's just how the C language works.

  • 0 in reply to Archaeologist
    Prodigy 70 points

    Just to close the loop on this.... I Did declare my variables as CONST.  I didn't want them to be modifiable and further, since I am using a microcontroller I wanted the strings stored in flash (.text).

    This form fails:

    const char szCompany[] = "MyCompany";

    This form works:

    const char *szCompany = "MyCompany";

    In my opinion, both forms should work.

  • 0 in reply to Normand Martel77
    TI__Guru* 84285 points
    Then do this:
    #pragma DATA_SECTION(szCompany, ".text:.strings")
    const char szCompany[] = "MyCompany";