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digitalmars.D.learn - How to use core.vararg to print D variadic arguments and their types

reply BoQsc <vaidas.boqsc gmail.com> writes:
https://dlang.org/phobos/core_vararg.html

The common way to use **va_arg** is `va_arg!(int)(_argptr);`
What would be the alternative way or syntax that behave exactly 
the same way, even if more verbose?



____
`va_arg!(int)(_argptr);` is taken from an example in:
https://dlang.org/spec/function.html#d_style_variadic_functions
Sep 14 2023
parent reply Basile B. <b2.temp gmx.com> writes:
On Thursday, 14 September 2023 at 15:19:29 UTC, BoQsc wrote:

 https://dlang.org/phobos/core_vararg.html

 The common way to use **va_arg** is `va_arg!(int)(_argptr);`
 What would be the alternative way or syntax that behave exactly 
 the same way, even if more verbose?



 ____
 `va_arg!(int)(_argptr);` is taken from an example in:
 https://dlang.org/spec/function.html#d_style_variadic_functions


here's how

```d
import core.vararg;

void main()
{
     foo(.5, 5);
}

void foo(...)
{
     int i = void;
     va_arg(_argptr, typeid(i), &i);
     assert(i == 5);
     double d = void;
     va_arg(_argptr, typeid(d), &d);
     assert(d == .5);
}
```
Sep 15 2023
parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 9/15/23 4:14 PM, Basile B. wrote:

 On Thursday, 14 September 2023 at 15:19:29 UTC, BoQsc wrote:

 https://dlang.org/phobos/core_vararg.html

 The common way to use **va_arg** is `va_arg!(int)(_argptr);`
 What would be the alternative way or syntax that behave exactly the 
 same way, even if more verbose?



 ____
 `va_arg!(int)(_argptr);` is taken from an example in:
 https://dlang.org/spec/function.html#d_style_variadic_functions


 
 here's how
 
 ```d
 import core.vararg;
 
 void main()
 {
      foo(.5, 5);
 }
 
 void foo(...)
 {
      int i = void;
      va_arg(_argptr, typeid(i), &i);
      assert(i == 5);
      double d = void;
      va_arg(_argptr, typeid(d), &d);
      assert(d == .5);
 }
 ```


Note that this doesn't work in gdc.

The templated version is actually more akin to what C does.

-Steve
Sep 16 2023
parent BoQsc <vaidas.boqsc gmail.com> writes:
 Note that this doesn't work in gdc.

 The templated version is actually more akin to what C does.


Yeah it does not seem to work in gdc when tested using 
https://d.godbolt.org/

The errors produced:

```
<source>:11:12: error: none of the overloads of template 
'core.stdc.stdarg.va_arg' are callable using argument types 
'!()(__va_list_tag[1], TypeInfo, int*)'
    11 |      va_arg(_argptr, typeid(i), &i);
       |            ^
/opt/compiler-explorer/gcc-trunk-20230917/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/
tdc/stdarg.d:179:7: note: Candidates are: 'va_arg(T)(ref va_list ap)'
   179 |     T va_arg(T)(ref va_list ap); // intrinsic
       |       ^
/opt/compiler-explorer/gcc-trunk-20230917/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/s
dc/stdarg.d:291:10: note:                 'va_arg(T)(ref va_list ap, ref T
parmn)'
   291 |     void va_arg(T)(ref va_list ap, ref T parmn); // 
intrinsic
       |          ^
<source>:14:12: error: none of the overloads of template 
'core.stdc.stdarg.va_arg' are callable using argument types 
'!()(__va_list_tag[1], TypeInfo, double*)'
    14 |      va_arg(_argptr, typeid(d), &d);
       |            ^
/opt/compiler-explorer/gcc-trunk-20230917/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/
tdc/stdarg.d:179:7: note: Candidates are: 'va_arg(T)(ref va_list ap)'
   179 |     T va_arg(T)(ref va_list ap); // intrinsic
       |       ^
/opt/compiler-explorer/gcc-trunk-20230917/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/s
dc/stdarg.d:291:10: note:                 'va_arg(T)(ref va_list ap, ref T
parmn)'
   291 |     void va_arg(T)(ref va_list ap, ref T parmn); // 
intrinsic
       |          ^
ASM generation compiler returned: 1
<source>:11:12: error: none of the overloads of template 
'core.stdc.stdarg.va_arg' are callable using argument types 
'!()(__va_list_tag[1], TypeInfo, int*)'
    11 |      va_arg(_argptr, typeid(i), &i);
       |            ^
/opt/compiler-explorer/gcc-trunk-20230918/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/
tdc/stdarg.d:179:7: note: Candidates are: 'va_arg(T)(ref va_list ap)'
   179 |     T va_arg(T)(ref va_list ap); // intrinsic
       |       ^
/opt/compiler-explorer/gcc-trunk-20230918/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/s
dc/stdarg.d:291:10: note:                 'va_arg(T)(ref va_list ap, ref T
parmn)'
   291 |     void va_arg(T)(ref va_list ap, ref T parmn); // 
intrinsic
       |          ^
<source>:14:12: error: none of the overloads of template 
'core.stdc.stdarg.va_arg' are callable using argument types 
'!()(__va_list_tag[1], TypeInfo, double*)'
    14 |      va_arg(_argptr, typeid(d), &d);
       |            ^
/opt/compiler-explorer/gcc-trunk-20230918/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/
tdc/stdarg.d:179:7: note: Candidates are: 'va_arg(T)(ref va_list ap)'
   179 |     T va_arg(T)(ref va_list ap); // intrinsic
       |       ^
/opt/compiler-explorer/gcc-trunk-20230918/lib/gcc/x86_64-linux-gnu/14.0.0/include/d/core/s
dc/stdarg.d:291:10: note:                 'va_arg(T)(ref va_list ap, ref T
parmn)'
   291 |     void va_arg(T)(ref va_list ap, ref T parmn); // 
intrinsic
       |          ^
Execution build compiler returned: 1
```
Sep 18 2023