c++, give input to dos prompt with command 'system'

i'm using c++ builder 6 and i'm writing a program here at work. this problem came up:
i want to decrypt a rsa private key in my program. now i can give one dos-command to the promptand will be executed fine:

AnsiString command.sprintf("openssl rsa -in %s -out %s",inputfile,outputfile);

after this line the command prompt waits for the password so i have to enter the password using the keyboard. i don(t want this i want to be able to pass the password to the command prompt so that my key will be decrypted without having to interfere manually.

if this cannot be done in C++ plz advise on a batch file that does the same...

greetz, drizzz
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>> if this cannot be done in C++ plz advise on a batch file that does the same...

Sure, this can be done in C/C++. Simply call the program with popen() instead of system. This allows you to write to the executed program's input stream. For example,

FILE *chkdsk;

if( (chkdsk = popen( command.c_str(), "wt" )) == NULL )
   exit( 1 );
fputs( "password", chkdsk );
printf( "\nProcess returned %d\r\n", pclose( chkdsk ) );

Replace "password" with the text you wish to enter.


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wrote this already in the duplicated question;-)

you can create a answer file and redirect stdin!!

TRy something like this(but i dont know if it will work with pwd):

echo testpwd > answer.txt
myapp.exe < answer.txt

Then when your prog read from stdin it will get the first line, second read->second line and so on!

>> wrote this already in the duplicated question;-)

Actually, you wrote it in the duplicate question, this one is the original. :-)

Besides, assuming this does work, it is still much simpler to use popen() because it returns a FILE pointer and you can write DIRECTLY into the sub process' stdin stream. :-)

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OK, Exceter your completly right, but ...

I tried to build a little Prog with popen, and the linker can't find this function!
So i tried it on a UNIX-Machine and it worked!

Are you sure this function is avaiable to DOS???

>> ...and the linker can't find this function!

popen() is found in stdio.h and, unless you are using C++, I doubt that you forgot to include this as you would not be able to write to stdout. What compiler are you using? If you are using a Microsoft compiler try placing an underscore before the function name. For example,

if( (chkdsk = _popen( command.c_str(), "wt" )) == NULL )


printf( "\nProcess returned %d\r\n", _pclose( chkdsk ) );

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