Thread: Can not use popen()

Hi, all
I try this code, but can not compile and debug

Code:

#include <stdio.h>

main()
   {
	   FILE *fp;
	   char line[130];			
   
	   fp = popen("netstat -n", "r");
					
	   while ( fgets( line, sizeof line, fp))
		{
		  printf("%s", line);
		}
	   pclose(fp);
   }

when i compile, console such as
Compiling...
OCMStart.c
D:\OCMStart\OCMStart.c(8) : warning C4013: 'popen' undefined; assuming extern returning int
D:\OCMStart\OCMStart.c(8) : warning C4047: '=' : 'struct _iobuf *' differs in levels of indirection from 'int '
D:\OCMStart\OCMStart.c(14) : warning C4013: 'pclose' undefined; assuming extern returning int

OCMStart.obj - 0 error(s), 3 warning(s)

When i debug, console such as

Linking...
OCMStart.obj : error LNK2001: unresolved external symbol _pclose
OCMStart.obj : error LNK2001: unresolved external symbol _popen
Debug/OCMStart.exe : fatal error LNK1120: 2 unresolved externals
Error executing link.exe.

OCMStart.exe - 3 error(s), 0 warning(s)


please help me to run this code

many thanks

Originally Posted by Salem

Since you seem to be using a Microsoft compiler, then try using
_popen
_pclose

If i use _popen and _pclose then this code can run on unix ?

Originally Posted by sistem

If i use _popen and _pclose then this code can run on unix ?

No. Thank Microsoft.

Thanks you very much,

please help me one again

When I use

#include <stdio.h>

Code:

main()
   {
	   FILE *fp;
	   char line[130];			
   
	   fp = _popen("netstat -n", "r");
					
	   while ( fgets( line, sizeof line, fp))
		{
		  printf("Output: %s", line);
		}
	   _pclose(fp);
   }

The result out put is correct :

Output :
Output : Active Connections
Output :
Output : Proto Local Address Foreign Address State
Output : TCP 127.0.0.1:1377 127.0.0.1:1378 ESTABLISHED
Output : TCP 127.0.0.1:1378 127.0.0.1:1377 ESTABLISHED
Output : TCP 127.0.0.1:1379 127.0.0.1:1380 ESTABLISHED
Output : TCP 127.0.0.1:1380 127.0.0.1:1379 ESTABLISHED
Output : TCP 127.0.0.1:1436 127.0.0.1:2628 ESTABLISHED
Output : TCP 127.0.0.1:2628 127.0.0.1:1436 ESTABLISHED
Output : TCP 172.16.2.89:1111 172.16.0.31:1745 ESTABLISHED
Output : TCP 172.16.2.89:1116 172.16.0.31:1498 CLOSE_WAIT
Output : TCP 172.16.2.89:1125 172.16.48.20:1026 ESTABLISHED
.................................................. .............

But I use java -version as below

Code:

main()
   {
	   FILE *fp;
	   char line[130];			
   
	   fp = _popen("java -version", "r");
					
	   while ( fgets( line, sizeof line, fp))
		{
		  printf("OUT PUT : %s", line);
		}
	   _pclose(fp);
   }

Result only : (do not run in while loop, have not string Output)

java version "1.4.2_12"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_12-b03)
Java HotSpot(TM) Client VM (build 1.4.2_12-b03, mixed mode)

Why when i use java -version, while loop do not run, seem that it is redundance

Originally Posted by matsp

It may be that the "java -version" is writing the output to "stderr", which means that it goes to the console, not the pipe.

If you want your code to compile on both Linux and Windows, you could do something like this:

Code:

#if WINDOWS
#define popen _popen
#endif

--
Mats

Could you please help me to put java -version command to a string ?

map your stderr of your prog to stdout..
since its called from your prog it ill use your programs fd's..
I hope this works..
else switch to execvp() it will definitely work fine..

Originally Posted by gibsosmat

map your stderr of your prog to stdout..
since its called from your prog it ill use your programs fd's..
I hope this works..
else switch to execvp() it will definitely work fine..

thanks you so much, I did as you and run ok on Windows

If i use _popen("java -version 2>&1", "r"); in my code and I build this code to abc.sh

Can this file run well on linux & mac OS ?

thanks

Can this file run well on linux & mac OS ?

If you have some program called "java" on Linux/Mac and you call popen() instead of _popen(), then yes.

Originally Posted by brewbuck

If you have some program called "java" on Linux/Mac and you call popen() instead of _popen(), then yes.

execvp(), can run all OS (Windows, Linux, Mac, Vista) ?

Originally Posted by sistem

execvp(), can run all OS (Windows, Linux, Mac, Vista) ?

Sure, but Windows has _popen(), others have popen(), so why not use it. If you use execvp() you have to deal with forking a new process, creating the pipes, reaping the process, etc, all of which popen() takes care of for you.