Question about type conversion and casting

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  • seia0106
    #1

    Question about type conversion and casting

    Hello
    I am writing a function to read a binary file. Here is a part of code
    #include <fstream>
    ..
    ..
    BYTE *pData;
    long lDataLen;
    pms->GetPointer(&pD ata);
    lDataLen = pms->GetSize();
    // Read one line at a time till end of file..
    if (m_inFile.getli ne(pData,
    lDataLen))pms->SetActualDataL ength(strlen((c har*)pData)+1);
    else {return S_FALSE;}
    ............... ....
    The error message that i get is this

    error C2664: 'class std::basic_istr eam<char,struct
    std::char_trait s<char> > &__thiscall std::basic_istr eam<char,struct
    std::char_trait s<char> >::getline(ch ar *,int)'
    : cannot convert parameter 1 from 'unsigned char *' to 'char *'
    Types pointed to are unrelated; conversion requires
    reinterpret_cas t, C-style cast or function-style cast

    Conflict in datatypes is causing this error. How can i solve this
    problem? Which type of casting is better here and how it should be
    used here.
    thanks
    Tags: None
    • John Harrison
      #2
      Re: Question about type conversion and casting


      "seia0106" <miahmed67@yaho o.com> wrote in message
      news:4fe296bd.0 307280854.7e7fa 0cb@posting.goo gle.com...[color=blue]
      > Hello
      > I am writing a function to read a binary file. Here is a part of code
      > #include <fstream>
      > .
      > .
      > BYTE *pData;
      > long lDataLen;
      > pms->GetPointer(&pD ata);
      > lDataLen = pms->GetSize();
      > // Read one line at a time till end of file..
      > if (m_inFile.getli ne(pData,
      > lDataLen))pms->SetActualDataL ength(strlen((c har*)pData)+1);
      > else {return S_FALSE;}
      > ............... ...
      > The error message that i get is this
      >
      > error C2664: 'class std::basic_istr eam<char,struct
      > std::char_trait s<char> > &__thiscall std::basic_istr eam<char,struct
      > std::char_trait s<char> >::getline(ch ar *,int)'
      > : cannot convert parameter 1 from 'unsigned char *' to 'char *'
      > Types pointed to are unrelated; conversion requires
      > reinterpret_cas t, C-style cast or function-style cast
      >
      > Conflict in datatypes is causing this error. How can i solve this
      > problem? Which type of casting is better here and how it should be
      > used here.
      > thanks[/color]

      Why are you trying getline in a binary file? getline is for text files.

      Anyway you can cast pData to the required type, one of the few common
      instances where a cast is justified.

      if (m_inFile.getli ne((char*)pData ,lDataLen))

      But the fact that you cast pData to (char*) twice, suggests that maybe you
      would do better to declare is as char* in the first place. After all it does
      appear to be text data, and char* is used for text.

      john



        Comment

        • seia0106
          #3
          Re: Question about type conversion and casting

          Thank you for the reply.
          The file is a text file. I have tried to do it the way you said but it
          is still not working. In this function *pData must be declared as a
          'BYTE'type. So how to use a 'BYTE' type *pData as a first parameter of
          getline() method and in strlen()? The error is same that
          "cannot convert parameter 1 from 'const char ** ' to 'unsigned char **
          '"

          I have looked into the text books for unsigned char type, char type
          and signed char type but I am little confused about their differences
          and uses.

          thanks in advance


          "John Harrison" <john_andronicu s@hotmail.com> wrote in message news:<bg3nk7$kp 9sp$1@ID-196037.news.uni-berlin.de>...[color=blue]
          > "seia0106" <miahmed67@yaho o.com> wrote in message
          > news:4fe296bd.0 307280854.7e7fa 0cb@posting.goo gle.com...[color=green]
          > > Hello
          > > I am writing a function to read a binary file. Here is a part of code
          > > #include <fstream>
          > > .
          > > .
          > > BYTE *pData;
          > > long lDataLen;
          > > pms->GetPointer(&pD ata);
          > > lDataLen = pms->GetSize();
          > > // Read one line at a time till end of file..
          > > if (m_inFile.getli ne(pData,
          > > lDataLen))pms->SetActualDataL ength(strlen((c har*)pData)+1);
          > > else {return S_FALSE;}
          > > ............... ...
          > > The error message that i get is this
          > >
          > > error C2664: 'class std::basic_istr eam<char,struct
          > > std::char_trait s<char> > &__thiscall std::basic_istr eam<char,struct
          > > std::char_trait s<char> >::getline(ch ar *,int)'
          > > : cannot convert parameter 1 from 'unsigned char *' to 'char *'
          > > Types pointed to are unrelated; conversion requires
          > > reinterpret_cas t, C-style cast or function-style cast
          > >
          > > Conflict in datatypes is causing this error. How can i solve this
          > > problem? Which type of casting is better here and how it should be
          > > used here.
          > > thanks[/color]
          >
          > Why are you trying getline in a binary file? getline is for text files.
          >
          > Anyway you can cast pData to the required type, one of the few common
          > instances where a cast is justified.
          >
          > if (m_inFile.getli ne((char*)pData ,lDataLen))
          >
          > But the fact that you cast pData to (char*) twice, suggests that maybe you
          > would do better to declare is as char* in the first place. After all it does
          > appear to be text data, and char* is used for text.
          >
          > john[/color]

            Comment

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