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digitalmars.D.learn - How to call a C function from D that takes a FILE * as an argument?

reply Joe <jma freedomcircle.com> writes:
The subject basically says it all. The C function uses the 
argument to call fprintf and also passes it to other functions 
where it's used to call fileno, fprintf or putc.
Jul 03 2018
parent reply Seb <seb wilzba.ch> writes:
On Wednesday, 4 July 2018 at 01:06:36 UTC, Joe wrote:

 The subject basically says it all. The C function uses the 
 argument to call fprintf and also passes it to other functions 
 where it's used to call fileno, fprintf or putc.


Like you would with C's fprintf 
(https://dlang.org/phobos/core_stdc_stdio.html#.fprintf).
For example, this is a valid D program:

---
void main(string[] args)
{
     import core.stdc.stdio;
     FILE* pFile;
     int n;
     char[100] name;

     pFile = fopen ("myfile.txt","w"); // string literals are 
zero-terminated
     for (n=0 ; n<3 ; n++)
     {
         puts("please, enter a name: ");
         gets(name.ptr);
         fprintf pFile, "Name %d [%-10.10s]\n",n+1,name.ptr);
     }
     fclose(pFile);
}
---

(example from http://www.cplusplus.com/reference/cstdio/fprintf)

So just add the declaration to your D file:

---
extern(C) void myCfunction(FILE* stream);
---

and as long as you link your program into the D binary, you 
should be good to go.
For larger C bases, tools like dstep or dpp can help translating 
C/C++ header files to D.
Jul 03 2018
parent reply Joe <jma freedomcircle.com> writes:
On Wednesday, 4 July 2018 at 01:58:15 UTC, Seb wrote:

 So just add the declaration to your D file:

 ---
 extern(C) void myCfunction(FILE* stream);
 ---


I do have a similar declaration in D.  It appears the problem is 
that the C program I'm trying to convert passes stdout as the 
argument and the D compiler complains somewhat like the following:


Error: function foo.main.myCfunction (shared(_IO_FILE)* stream) 
is not callable using argument types (File)

So I guess the question is what to pass instead of stdout.
Jul 03 2018
parent reply Seb <seb wilzba.ch> writes:
On Wednesday, 4 July 2018 at 02:08:11 UTC, Joe wrote:

 On Wednesday, 4 July 2018 at 01:58:15 UTC, Seb wrote:

 So just add the declaration to your D file:

 ---
 extern(C) void myCfunction(FILE* stream);
 ---


 I do have a similar declaration in D.  It appears the problem 
 is that the C program I'm trying to convert passes stdout as 
 the argument and the D compiler complains somewhat like the 
 following:


 Error: function foo.main.myCfunction (shared(_IO_FILE)* stream) 
 is not callable using argument types (File)

 So I guess the question is what to pass instead of stdout.


Hmm, calling e.g. fprintf with stdout should just work:

---
void main()
{
     import core.stdc.stdio;
     fprintf(stdout, "Hello %s", "world".ptr);
}
---

Could you maybe provide your whole code?
Jul 03 2018
parent reply Joe <jma freedomcircle.com> writes:
On Wednesday, 4 July 2018 at 02:16:00 UTC, Seb wrote:

 Hmm, calling e.g. fprintf with stdout should just work:

 ---
 void main()
 {
     import core.stdc.stdio;
     fprintf(stdout, "Hello %s", "world".ptr);
 }
 ---

 Could you maybe provide your whole code?


This short test program shows the error:

---
import std.stdio;


void main()
{
     extern (C) void list(FILE *fd);
     list(stdout);
}
---

Now I fixed this by changing the import to core.stdc.stdio. I 
guess the problem is if you import std.stdio (which brings in the 
other one), there are two slightly incompatible stdout's and the 
D takes precedence.
Jul 03 2018
next sibling parent Adam D. Ruppe <destructionator gmail.com> writes:
On Wednesday, 4 July 2018 at 02:54:47 UTC, Joe wrote:

 Now I fixed this by changing the import to core.stdc.stdio. I 
 guess the problem is if you import std.stdio (which brings in 
 the other one), there are two slightly incompatible stdout's 
 and the D takes precedence.


If you import both modules (or even I think if just the D 
std.stdio, since it publicly imports the other), you can specify 
the C one by using its full name:

core.stdc.stdio.stdout

where you use it. of course you can also alias it to something 
shorter.
Jul 03 2018
prev sibling parent WebFreak001 <d.forum webfreak.org> writes:
On Wednesday, 4 July 2018 at 02:54:47 UTC, Joe wrote:

 On Wednesday, 4 July 2018 at 02:16:00 UTC, Seb wrote:

 Hmm, calling e.g. fprintf with stdout should just work:

 ---
 void main()
 {
     import core.stdc.stdio;
     fprintf(stdout, "Hello %s", "world".ptr);
 }
 ---

 Could you maybe provide your whole code?


 This short test program shows the error:

 ---
 import std.stdio;


 void main()
 {
     extern (C) void list(FILE *fd);
     list(stdout);
 }
 ---

 Now I fixed this by changing the import to core.stdc.stdio. I 
 guess the problem is if you import std.stdio (which brings in 
 the other one), there are two slightly incompatible stdout's 
 and the D takes precedence.


`stdout.getFP` (stdout is of the D std.stdio.File struct type and 
with getFP you get the underlying FILE*)
Jul 04 2018