problem with templates

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  • kalki70
    #1

    problem with templates

    Hi,

    I'm working with templates, but I have a syntax problem I don't know
    how to fix.

    I built a small example, so maybe you can tell me how to write
    correctly this code.

    I have 2 files : template.H and template.C

    Template.H :

    #ifndef _TEMPLATE_H_739 832983298
    #define _TEMPLATE_H_739 832983298

    template <class T>
    class MyTemplate
    {
    class OtherClass
    {
    int foo;
    };
    T value;

    public:
    OtherClass changeValue(Oth erClass newValue);
    };

    #endif

    Template.C :

    #include <template.H>

    template <class T>
    MyTemplate< T >::OtherClass MyTemplate< T >::changeValue( MyTemplate< T
    >::OtherClass newValue)
    {
    return newValue;
    }

    Here is my problem, I don't know how to make the definition of method
    changeValue().
    If it returns and receives a simple parameter, like int, I have no
    problem, but the return type and parameter type is another class
    defined inside MyTemplate.

    Working in Solaris, compiling with CC I get the following warning.
    "/home/usuarios/lrojas/engine2.5/src/template.C", line 4: Warning
    (Anachronism): Type names qualified by template parameters require
    "typename".
    "/home/usuarios/lrojas/engine2.5/src/template.C", line 4: Warning
    (Anachronism): Type names qualified by template parameters require
    "typename".

    In Linux/g++ it doesn't even compile, it generates an error instead of
    a warning.

    template.C:4: error: expected constructor, destructor, or type
    conversion before "MyTemplate "

    What is the right syntax to define methods for MyTemplate, when I need
    to use a parameter type defined inside MyTemplate, like "OtherClass " ?

    I've been reading some tutorials on templates in internet, but couldn't
    find this situation.

    Thanks for any advice!

    Luis

    Tags: None
    • Victor Bazarov
      #2
      Re: problem with templates

      kalki70 wrote:
      I'm working with templates, but I have a syntax problem I don't know
      how to fix.
      >
      I built a small example, so maybe you can tell me how to write
      correctly this code.
      >
      I have 2 files : template.H and template.C
      >
      Template.H :
      >
      #ifndef _TEMPLATE_H_739 832983298
      Any names that start with an underscore and a capital letter are
      reserved by the implementation. IOW, do _not_ use them, you are
      not allowed to. Why do you think you need the leading underscore
      here?
      #define _TEMPLATE_H_739 832983298
      >
      template <class T>
      class MyTemplate
      {
      class OtherClass
      {
      int foo;
      };
      T value;
      >
      public:
      OtherClass changeValue(Oth erClass newValue);
      };
      >
      #endif
      >
      Template.C :
      >
      #include <template.H>
      >
      template <class T>
      MyTemplate< T >::OtherClass MyTemplate< T >::changeValue( MyTemplate< T
      >::OtherClass newValue)
      Try not to post wrapped text that starts with ">" or a similar character
      used in quoting.
      {
      return newValue;
      }
      >
      Here is my problem, I don't know how to make the definition of method
      changeValue().
      You almost did it right. What you need is to place 'typename' in two
      places in the "head" of that function:

      template<class T>
      typename MyTemplate<T>:: Otherclass // <- there
      MyTemplate<T>:: changeValue(
      typename MyTemplate<T>:: OtherClass newValue) // <- there
      {
      return newValue;
      }
      If it returns and receives a simple parameter, like int, I have no
      problem, but the return type and parameter type is another class
      defined inside MyTemplate.
      >
      Working in Solaris, compiling with CC I get the following warning.
      "/home/usuarios/lrojas/engine2.5/src/template.C", line 4: Warning
      (Anachronism): Type names qualified by template parameters require
      "typename".
      "/home/usuarios/lrojas/engine2.5/src/template.C", line 4: Warning
      (Anachronism): Type names qualified by template parameters require
      "typename".
      >
      In Linux/g++ it doesn't even compile, it generates an error instead of
      a warning.
      >
      template.C:4: error: expected constructor, destructor, or type
      conversion before "MyTemplate "
      >
      What is the right syntax to define methods for MyTemplate, when I need
      to use a parameter type defined inside MyTemplate, like "OtherClass " ?
      You need 'typename' there.
      I've been reading some tutorials on templates in internet, but
      couldn't find this situation.
      Read the FAQ.

      V
      --
      Please remove capital 'A's when replying by e-mail
      I do not respond to top-posted replies, please don't ask


        Comment

        • kalki70
          #3
          Re: problem with templates

          THANKS!!!

          Victor Bazarov wrote:
          kalki70 wrote:
          I'm working with templates, but I have a syntax problem I don't know
          how to fix.

          I built a small example, so maybe you can tell me how to write
          correctly this code.

          I have 2 files : template.H and template.C

          Template.H :

          #ifndef _TEMPLATE_H_739 832983298
          >
          Any names that start with an underscore and a capital letter are
          reserved by the implementation. IOW, do _not_ use them, you are
          not allowed to. Why do you think you need the leading underscore
          here?
          >
          #define _TEMPLATE_H_739 832983298

          template <class T>
          class MyTemplate
          {
          class OtherClass
          {
          int foo;
          };
          T value;

          public:
          OtherClass changeValue(Oth erClass newValue);
          };

          #endif

          Template.C :

          #include <template.H>

          template <class T>
          MyTemplate< T >::OtherClass MyTemplate< T >::changeValue( MyTemplate< T
          >::OtherClass newValue)
          >
          Try not to post wrapped text that starts with ">" or a similar character
          used in quoting.
          >
          {
          return newValue;
          }

          Here is my problem, I don't know how to make the definition of method
          changeValue().
          >
          You almost did it right. What you need is to place 'typename' in two
          places in the "head" of that function:
          >
          template<class T>
          typename MyTemplate<T>:: Otherclass // <- there
          MyTemplate<T>:: changeValue(
          typename MyTemplate<T>:: OtherClass newValue) // <- there
          {
          return newValue;
          }
          >
          If it returns and receives a simple parameter, like int, I have no
          problem, but the return type and parameter type is another class
          defined inside MyTemplate.

          Working in Solaris, compiling with CC I get the following warning.
          "/home/usuarios/lrojas/engine2.5/src/template.C", line 4: Warning
          (Anachronism): Type names qualified by template parameters require
          "typename".
          "/home/usuarios/lrojas/engine2.5/src/template.C", line 4: Warning
          (Anachronism): Type names qualified by template parameters require
          "typename".

          In Linux/g++ it doesn't even compile, it generates an error instead of
          a warning.

          template.C:4: error: expected constructor, destructor, or type
          conversion before "MyTemplate "

          What is the right syntax to define methods for MyTemplate, when I need
          to use a parameter type defined inside MyTemplate, like "OtherClass " ?
          >
          You need 'typename' there.
          >
          I've been reading some tutorials on templates in internet, but
          couldn't find this situation.
          >
          Read the FAQ.
          >
          V
          --
          Please remove capital 'A's when replying by e-mail
          I do not respond to top-posted replies, please don't ask

            Comment

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