Looking for a hack to redirect command output to variable file name.

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This is NOT a problem , just a curiosity question.
The attached C++ code creates "temp_file.txt " file.

I am curious if there is a hack to use variable instead of "literal (?) " for the file name.
My guess woudl be to modify the "hciconfig" redirecting command, but I am not that versed in doing so.

system("hciconfig -a > temp_file.txt ");

What I have tried:

Replacing the file name with variable ( char *) as file name did not give expected results.

Posted 17-Feb-20 3:45am

Vaclav_

Updated 17-Feb-20 3:57am

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CPallini · Accepted Answer · 2020-02-17T03:52:00

The argument of system is a string, you may generate such a string according to your needs.
For instance the following program

C++

#include <iostream>
#include <sstream>
#include <vector>
using namespace std;

int main()
{
  vector <const char *> names { "foo.txt", "boo.txt", "gooooo.txt" };

  for (const auto & name : names )
  {
    ostringstream oss;
    oss <<   "hciconfig -a > " << name;
    cout << oss.str() << endl; // here you are the customized command string
  }
}

produces

hciconfig -a > foo.txt
hciconfig -a > boo.txt
hciconfig -a > gooooo.txt

Richard MacCutchan · Accepted Answer · 2020-02-17T03:58:00

Solution 2

It's just basic C string manipulation ...

C++

char* command = "hciconfig -a > ";
char* tempfile = "temp_file.txt";
char szFullCommand[64];
strcpy(szFullCommand, command);
strcat(szFullCommand, tempfile);
system(szFullCommand);

Posted 17-Feb-20 3:58am

Richard MacCutchan

Comments

Vaclav_ 17-Feb-20 11:08am

Both nice solutions, but...
it's the terminology which is puzzling
"char *" is a string in C
and
"string" x is a string in C++
Thanks

Richard MacCutchan 17-Feb-20 11:52am

C++ enhanced things by creating basic classes to make it more object oriented. But it still supports the C types. If you are writing C++ code then you should really use only C++ classes for any compound objects (e.g. string).

Strictly speaking char* is a pointer to an array of char types, not a string, as C does not have any concept of compound types.