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 | Posted by thinkunix
in reply to DLearner |  Permalink Reply |
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thinkunix 
Posted in reply to DLearner
| DLearner via Digitalmars-d-learn wrote:
> Wanted to try out linking two source files independantly compiled.
>
> ExtCallee.d source file:
> ```
> extern(C) void ExtCallee() {
> import std.stdio;
>
> writeln("Entered: ", __FUNCTION__);
> writeln("Exiting: ", __FUNCTION__);
> }
> ```
> ExtMain.d source file:
> ```
> void main() {
> import std.stdio;
> extern(C) void ExtCallee();
>
>
> writeln("Entered: ", __FUNCTION__);
>
> ExtCallee();
>
> writeln("Exiting: ", __FUNCTION__);
> }
What is the advantage of using extern(C)?
Since both are D source files, why wouldn't you do just this:
```d
// ExtCallee.d
void ExtCallee()
{
import std.stdio;
writeln("Entered: ", __FUNCTION__);
writeln("Exiting: ", __FUNCTION__);
}
```
```d
// ExtMain.d
void main()
{
import std.stdio;
import ExtCallee;
writeln("Entered: ", __FUNCTION__);
// I had to scope this to get it to compile
// If instead I put the function in myfn.d and
// did "import myfn;" it works without the scope operator.
ExtCallee.ExtCallee();
writeln("Exiting: ", __FUNCTION__);
}
```
Compile with:
$ dmd ExtCallee.d ExtMain.d -of=prog
Without extern(C), the linker mangles names:
$ nm ExtCallee.o | grep ExtCallee
0000000000000000 R _D9ExtCallee12__ModuleInfoZ
0000000000000000 W _D9ExtCalleeQkFZv
$ nm ExtMain.o | grep ExtCallee
U _D9ExtCalleeQkFZv
With extern(C), the linker does not mangle names:
$ nm ExtCallee.o | grep ExtCallee
0000000000000000 W ExtCallee
0000000000000000 R _D9ExtCallee12__ModuleInfoZ
$ nm ExtMain.o | grep ExtCallee
U ExtCallee
If not calling C code, why use extern(C) for D code?
scot
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