<div>
I'm not an expert, but let's try<br />
<br />
--------------------------<wbr />-------<br />
extern float a;<br />
This is a declaration, because you don't initialize the value of a.<br />
<br />
--------------------------<wbr />-------<br />
namespace mystd = std;<br />
<br />
This way you make an alias of the namepace. Compare it to this:<br />
<br />
namespace mynamespace<br />
{<br />
&nbsp; &nbsp; &nbsp; &nbsp;...<br />
}<br />
<br />
Here the namespace is both declared and defined.<br />
<br />
--------------------------<wbr />-------<br />
typedef unsigned char byte;<br />
It is a type definition and has nothing to do with variable, function etc. declarations/definitions or namespace aliases.
</div>


I'm not an expert, but let's try

---------------------------------
extern float a;
This is a declaration, because you don't initialize the value of a.

---------------------------------
namespace mystd = std;

This way you make an alias of the namepace. Compare it to this:

namespace mynamespace
{
       ...
}

Here the namespace is both declared and defined.

---------------------------------
typedef unsigned char byte;
It is a type definition and has nothing to do with variable, function etc. declarations/definitions or namespace aliases.

<div>
I am sort of confused here .... because based on<br />
&quot;C++ in a nutshell&quot; p24 and p28 .... typedef is only a declaration ?? I don't know if I miss understand it here.....<br />
since this original question ask which of the three is a definition.... then I don't &nbsp;know if &quot;namespace = std&quot; &nbsp;a definition<br />
or not ... ? <br />
thanks.
</div>


I am sort of confused here .... because based on
"C++ in a nutshell" p24 and p28 .... typedef is only a declaration ?? I don't know if I miss understand it here.....
since this original question ask which of the three is a definition.... then I don't  know if "namespace = std"  a definition
or not ... ?
thanks.

<div>
<div class="content wysiwyg-content">
To C++ expert ?<br />
<br />
&nbsp; &nbsp;Is &quot;extern float a&quot; a declaration ?<br />
&nbsp; &nbsp;Is the &quot;namespace mystd = std&quot; a declaration ? definition ? or alias ?<br />
<br />
&nbsp; &nbsp;Also, is the &quot;tydef unsigned char byte&quot; a declaration ? definition ? or alias ?<br />
<br />
&nbsp; &nbsp;Thanks a lot !<br />
<br />
meow .....
</div>
</div>


To C++ expert ?

   Is "extern float a" a declaration ?
   Is the "namespace mystd = std" a declaration ? definition ? or alias ?

   Also, is the "tydef unsigned char byte" a declaration ? definition ? or alias ?

   Thanks a lot !

meow .....

C++ : declaration ? definition ? alias ?

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