6 
The C function, RetReal.c
The Pascal main program, RetRealMain.p
The commands to compile and execute RetReal.c and RetRealMain.p
double RetReal(double *x)
{
return(*x + 1.0);
}
program RetRealMain; var
r, s: real;
function RetReal(var x: real): real; external c;
begin
r := 2.0;
s := RetReal(r); writeln(r: 4: 1, s: 4: 1)
end. { RetRealMain }
hostname% cc
hostname% pc RetReal.o RetRealMain.p hostname% a.out
2.0 3.0
Pascal has a special type that is a pointer to a procedure. A variable of this type can be used as a parameter, as follows:
The C function, ProcPar.c | #include <string.h> |
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| void proc_c (void (*p)()) | /* a pointer to procedure argument */ |
| { |
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| char *s ; |
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| s = "Called from C"; |
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| (*p)( s, strlen(s)); | /* Call the Pascal routine */ |
| } |
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The | 131 |