Use ReturnValue from C Program in Java Program !!!
Hi:
I want to calculate n! in a C program. This program expects an int as argument and returns result as a long. I want to start this C program from java. I have to transfer argument to the program and expect return valu, which I want to show on the screen in my java programm. Here is my C-Program:
#include <stdlib.h>
#include <stdio.h>
long f(int n)
{
if (n<1)
return 1;
else
return n * f(n-1);
}
int main(int argcnt, char* argc[])
{
if (argcnt < 2)
return -1;
else
{
int n = atoi(argc[1]);
if (n<0)
return -1;
else
return f(n);
}
}
This program works fine in C. Now, I want to do followng:
// Call this program
Process p = Runtime.getRuntime().exec("C:\\Temp\\calcfak.exe, 5");
// C-Program calculates 5! = 120 and returns this. How to get this value ?
Thanks for any help.
[1776 byte] By [
pitalica] at [2007-9-26 4:05:20]
Hi,
my suggestion:Process p = Runtime.getRuntime().exec("C:\\Temp\\calcfak.exe 5");
p.waitFor();
int ret = p.exitValue();
Java int is 32 bits. It will be the same range as C long (depends on your machine however).
Regards,
Martin
Er, I don't think exitValue() will get the original poster what they want. If a process terminates normally, then exitValue() returns zero. That's probably not a desirable outcome.Cheers!
amolk at 2007-6-29 13:04:39 >
Reply to amolk.
In C the return x from main is equivalent to exit(x).
And the C program of the original poster use x to return the function value (or -1 on error). So it may be read with p.exitValue(). The zero value for success is only a convention and this program don't use it.
Regards,
Martin
Hi Petar! The i/o streams associated with the java.lang.Process class deal w/ the standard i/o streams. So, if your C program prints the computed value to the standard output, you can acccess that using the mechanism I described earlier.
If you do run into difficulties, could you possibly post some code so folks here can take a look at it?
Cheers!
amolk at 2007-6-29 13:04:39 >
Hi Petar! Sorry, forgot one point. You said you wanted to invoke the C program as follows.
Process p = Runtime.getRuntime().exec("C:\\Temp\\calcfak.exe, 5");
If your C program is going to read the input as a command line argument, then you need to remove the comma in the argument to exec().
Hope this helps!
Cheers!
amolk at 2007-6-29 13:04:39 >
>Thanks. Unhappily, it doesn't work. I become zero back. Any other idea?Yes. Your C program should use a long type as follows:long main(int argcnt, char* argc[])BTW: why does you do such strange things? Why not using Java only?Regards,Martin
Thanks for your replay.I tryed with long type, but it doesn't work too. >BTW: why does you do such strange things? Why not using Java only?Nun, I want to know, is it posibile and if yes, hot ist to do it. Any other idea?
