Running a c/c++ program from java through command line

Question

I have written a java program that compiles and executes C,c++,java programs ..I firstly tested it for java and it worked absolutely fine. Then I tested it for C but it gave errors.Please tell what I need to do..Here is the module which compiles the code..:

public void compileCode(String path,String lang)throws IOException
    {
        String cmd="";
        if(lang.equals("c")||lang.equals("cpp"))
            cmd="g++ Main"+threadNum+"."+lang+" -o "+threadNum;
        else if(lang.equals("java"))
            cmd="javac Main"+threadNum+".java";

        Process p=Runtime.getRuntime().exec(cmd,null,new File(path));

         String s=null;
        BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));
        while ((s = stdError.readLine()) != null) {
            msg+=s+"\n";
            res=0;
        }
        if(res!=0)
            processCode(path,lang);
    }

And the error is :

Exception in thread "main" java.io.IOException: Cannot run program "g++" (in directory "C:\wamp\www\usercodes\lokesh"): CreateProcess error=2, The system cannot find the file specified
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)
    at java.lang.Runtime.exec(Runtime.java:615)
    at java.lang.Runtime.exec(Runtime.java:448)
    at Contest.compileCode(Main.java:164)
    at Contest.makeFile(Main.java:154)
    at Contest.main(Main.java:52)
    at Main.main(Main.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:1

20)

I can run the g++ filename.c -o file from the command promt . Is there anything else I need ? C:\wamp\www\usercodes\lokesh>echo %PATH% C:\Program Files (x86)\Java\jdk1.7.0\bin;C:\Program Files (x86)\CodeBlocks\MinGW \bin — Wayne Rooney
– Wayne Rooney, Commented Jun 29, 2012 at 20:22
This isn't really relevant to your question, but why do this? — Dave
– Dave, Commented Jun 29, 2012 at 22:39

Arne · Accepted Answer · 2012-06-29 21:22:58Z

2

For "g++" to work, there has to be a g++.exe on the PATH for windows. If it is a "g++.bat" or "g++.cmd", you have to call Runtime.exec with the exact name.

answered Jun 29, 2012 at 21:22

Arne

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8 Comments

Wayne Rooney Over a year ago

No..I have a g++.exe on the path ..But its still dosent work..But if any other command(not necessay) g++ can do the trick u can tell me that also

Arne Over a year ago

Runtime.exec appends ".exe" to find and start an executable that was given without extension. But Runtime.exec does not try the cmd or bat extension. Are you shure there is a g++.exe?

Wayne Rooney Over a year ago

Yes I am sure..If u dont believe u can see my screenlink

Arne Over a year ago

fine ;-). Do you have Sources for your jdk 7? Then have a look at ProcessBuilder Line 1029. That's where your exception comes from.

Wayne Rooney Over a year ago

here it is:[link]hg.openjdk.java.net/jdk7/jdk7-gate/jdk/file/e947a98ea3c1/src/… But I think there is a problem with the C compiler because java programs are running fine

|

Wayne Rooney · Accepted Answer · 2012-06-29 22:50:29Z

0

I used process Builder instead and it worked out..Anyways thnx for ur time :) Here's the code...

public void compileCode(String path,String lang)throws IOException,InterruptedException
    {
        String cmd="";
        if(lang.equals("c")||lang.equals("cpp"))
            cmd="g++ "+path+"Main"+threadNum+"."+lang+" -o "+threadNum;
        else if(lang.equals("java"))
            cmd="javac Main"+threadNum+".java";
        ProcessBuilder process=new ProcessBuilder();
        process.directory(new File(path));
        process.command(new String[]{"cmd","/c",cmd});
        Process p=process.start();
        String s=null;
        BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));
        while ((s = stdError.readLine()) != null) {
            msg+=s+"\n";
            res=0;
        }
        if(res!=0)
            processCode(path,lang);
    }

answered Jun 29, 2012 at 22:50

Wayne Rooney

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3 Comments

Arne Over a year ago

in this version cmd.exe finds and starts g++. just to point out the difference.

Wayne Rooney Over a year ago

But unfortunately I have a problem here.. In the next module where I run the code , the .exe file does not destroy when I use this: ProcessBuilder process=new ProcessBuilder();process.directory(new File(path));Process p=process.start(); p.destroy();

Wayne Rooney Over a year ago

Ok ..I found out that this process is not destrying because the process is actually cmd and that is creating a subprocess which I am not destroying..

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