I have created dll in golang want to use inside lazarus freepascal

[Packs]

Code: C  [Select][+][-]

1. package main
2.  
3. import "C"
4. import (
5.         "fmt"
6.         "math"
7. )
8.  
9.  
10. // export RoundFloat
11. func RoundFloat(val float64, precision uint) float64 {
12.         ratio := math.Pow(10, float64(precision))
13.         return math.Round(val*ratio) / ratio
14. }
15.  
16.  
17. func main() {
18. }
19.  
20.  

this is the command for compile the code in golang
go build -o easy.dll -buildmode=c-shared main.go

I would like to use the dll inside the lazarus free pascal

[Zvoni]

What'S the calling convention? cdecl? Something else?

[srvaldez]

in line 10 you have: // export RoundFloat
you need to remove the space between // and export otherwise it will not export the function

[srvaldez]

example

Code: Pascal  [Select][+][-]

1. {$mode objfpc}{$h+}
2.  
3. program easy_dll_test;
4.  
5. function RoundFloat(x:double; prec:integer): double; cdecl; external 'easy' name 'RoundFloat';
6.  
7. var
8.         x, y:double;
9.         prec:integer;
10.        
11. begin
12.         x:=3.1415926535897932;
13.         prec:=4;
14.         y:=RoundFloat(x, prec);
15.         writeln(y);
16. end.
17.  

output: 3.1415999999999999E+000

[Packs]

Thank you .

It is working

function abcRoundFloat(val: Double; precision: UInt8) :Double ;  external 'easy.dll' name 'RoundFloat';

Y := abcRoundFloat(12.345,2); 

[Packs]

Code: Pascal  [Select][+][-]

1.  
2. //export HelloWorld
3. func HelloWorld(sString *C.char) *C.char {
4.         xyz := C.GoString(sString)
5.         return C.CString("Hello " + xyz)
6. }
7.  
8.  

I want my function should return me string value .

Code: Pascal  [Select][+][-]

1.  
2. function abcHelloWorld(xyz: string): string;
3.   external 'easy.dll' Name 'HelloWorld';
4.  
5.   xyz := abcHelloWorld('abcd');
6.   DebugLn('hello world : ' + xyz);
7.  

it is not returning string value .

[cdbc]

Hi
Try this:

Code: Pascal  [Select][+][-]

1. function HelloWorld(xyz: pchar): pchar;
2.   external 'easy.dll' Name 'HelloWorld';
3.  
4.   xyz := string(HelloWorld(pchar('abcd')));
5.   DebugLn('hello world : ' + xyz);

Regards Benny

[Packs]

Thank you Sir . it is working .

Code: Pascal  [Select][+][-]

1. func Overallcgpa_Array(arr_data []float64, arr_size int, config_point int) *C.char {
2.  
3.  
4.         var (
5.                 i       int
6.                 Totalcg float64
7.         )
8.         myRoundFloat := func(val float64, precision uint) float64 {
9.                 //https://gosamples.dev/round-float/
10.  
11.                 ratio := math.Pow(10, float64(precision))
12.  
13.                 return math.Round(val*ratio) / ratio
14.         }
15.  
16.         for i = 0; i < arr_size-1; i++ {
17.                 Totalcg += arr_data[i]
18.         }
19.  
20.  
21.         cgpa := myRoundFloat(Totalcg/float64(config_point), 2)
22.  
23.         scgpa := fmt.Sprintf("%.2f", cgpa)
24.  
25.  
26.         return C.CString(scgpa)
27. }
28.  

Code: Pascal  [Select][+][-]

1. function Overallcgpa_Array(Array_data: array of real; array_size: integer;
2.   precision: int64): PChar; external 'easy.dll' Name 'Overallcgpa_Array';
3.  
4.   SArray[1] := 8.42;
5.   SArray[2] := 9.25;
6.   SArray[3] := 9.17;
7.   SArray[4] := 9.83;
8.   SArray[5] := 0.0;
9.   SArray[6] := 0.0;
10.  
11.   xyz := string(Overallcgpa_Array(SArray, 6, nConfigPoint));
12.   DebugLn('Overallcgpa_array : ' + xyz);
13.  
14.  
15.  

what is the issue in my code . it is giving me access violoation error

[bytebites]

array of double, int, int  versus array of real, int, int64

[cdbc]

Hi
...and maybe (building on bytebites) call it like this:

Code: Pascal  [Select][+][-]

1. xyz := string(Overallcgpa_Array(SArray[1], 6, nConfigPoint));
2.   DebugLn('Overallcgpa_array : ' + xyz);

To me, it seems to be the array-data and not the array-pointer... the 'go' func accepts 
Regards Benny

[marcov]

Is it a C array (a pointer) or a Pascal open array?

[Packs]

Dear Team,

Please guide me what is mistake in my code

Code: Pascal  [Select][+][-]

1.  
2.           DebugLn('Table Value ---------------- ');
3.           DebugLn('first ' + floattostr(vt_column.FieldByName('mul_sgpa_ce1').AsFloat));
4.           DebugLn('second ' + floattostr(vt_column.FieldByName('mul_sgpa_ce2').AsFloat));
5.           DebugLn('third ' + floattostr(vt_column.FieldByName('mul_sgpa_ce3').AsFloat));
6.           DebugLn('four ' + floattostr(vt_column.FieldByName('mul_sgpa_ce4').AsFloat));
7.                  
8.         nConfigPoint := MyQ_batchexam.FieldByName('Overallcreditpoints').AsInteger;
9.         DebugLn('nConfigPoint ' + floattostr(nConfigPoint));
10.  
11.  
12.         DebugLn('forumla ' + '(Fsgpa_tot / nConfigPoint)');
13.         Fcgpa_round := (Fsgpa_tot / nConfigPoint);
14.         DebugLn('forumla value ' + floattostr(Fcgpa_round));
15.         //DebugLn(Pasfilename + 'Fcgpa_round ' + floattostr(Fcgpa_round));
16.  
17.         DebugLn('golang round founction : ' + 'RoundFloat(Fcgpa_round, 2)');
18.         Round_value := RoundFloat(Fcgpa_round, 2);
19.         DebugLn('Golang round ' + floattostr(Round_value));
20.  
21.         DebugLn('Hard Coded values ------------------ ' );
22.         nConfigPoint := 96 ;
23.         DebugLn('nConfigPoint : ' + FloatToStr(nConfigPoint));
24.  
25.         Fsgpa_tot := 211.92 + 211.92 + 216 + 240;
26.         DebugLn('Hard coded Total value : ' + FloatToStr(Fsgpa_tot));
27.  
28.         DebugLn('forumla ' + '(Fsgpa_tot / nConfigPoint)');
29.         Fcgpa_round := (Fsgpa_tot / nConfigPoint);
30.         DebugLn('Hard coded  Fcgpa_round : ' + FloatToStr(Fcgpa_round));
31.  
32.         DebugLn('golang round founction : ' + 'RoundFloat(Fcgpa_round, 2)');
33.         Round_value := RoundFloat(Fcgpa_round, 2);
34.         DebugLn('Golang round : ' + FloatToStr(Round_value));
35.  
36.  

Code: Text  [Select][+][-]

1. Table Value ----------------
2. first 211.92
3. second 211.92
4. third 216
5. four 240
6. Total 879.84
7. nConfigPoint 96
8. forumla (Fsgpa_tot / nConfigPoint)
9. forumla value 9.165
10. golang round founction : RoundFloat(Fcgpa_round, 2)
11. Golang round 9.17
12. Hard Coded values ------------------
13. nConfigPoint : 96
14. Hard coded Total value : 879.84
15. forumla (Fsgpa_tot / nConfigPoint)
16. Hard coded  Fcgpa_round : 9.165
17. golang round founction : RoundFloat(Fcgpa_round, 2)
18. Golang round : 9.16
19.  
20.  

It is returning two different value .
I have shared the log details too.

Code: Pascal  [Select][+][-]

1. //export RoundFloat
2. func RoundFloat(val float64, precision uint) float64 {
3.         //https://gosamples.dev/round-float/
4.         ratio := math.Pow(10, float64(precision))
5.         return math.Round(val*ratio) / ratio
6. }
7.  

Shared Golang code too

I should get answer 9.16 from table value it is giving 9.17

[dseligo]

IMHO, problem is that floating point values can't be represented exactly.
When you calculate Fsgpa_tot, some small errors starts to accumulate (very small, in order 10e-13 or 10e-14), and results probably goes just a tiny bit over 9,165, enough to round it to 9,17.
When you try with hard coded values, compiler calculates Fsgpa_tot in advance, maybe using single precision or maybe just different order. Now results goes just a tiny bit under 9,165, resulting in rounding to 9,16.

Try to add this after line 15 to see if this is what is going on:

Code: Pascal  [Select][+][-]

1.   WriteLn('Total - 879.84 = ' + floattostr(Fsgpa_tot - 879.84));
2.   WriteLn('Formula - 9.165 = ' + floattostr(Fcgpa_round - 9.165));

P.S.:
Why aren't you using Free Pascal's rounding functions?

[Packs]

Application is written in golang.

And we are creating report in Lazarus.

So in this part of the application there is formula.

So we have used same golang formula

[Packs]

I have created demo application. it is working properly .
but on main application it is not working .
I am not getting any clue to solve this issue .