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Reply to topic   Topic: How can I write to a file in an c++ Apache module?

Joined: 13 Jan 2018
Posts: 1
Location: Portugal, Lisbon

PostPosted: Sun 14 Jan '18 0:52    Post subject: How can I write to a file in an c++ Apache module? Reply with quote

Hi all

I have the following code, in C++ (in Ubuntu 16.04) for an Apache HTTP Server module.

I would like to write some debug to logs (using std::ofstream), but I don't see anything. Neither the logs, or the files.


#include <httpd.h>
#include <http_log.h>
#include <http_core.h>
#include <http_protocol.h>
#include <http_request.h>

#include <apr_strings.h>

#include <iostream>
#include <fstream>

void write_something_to_a_file(const std::string& path) // <---- DOESN'T WRITE TO FILE!
   std::ofstream myfile (path);
   if (myfile.is_open())
      myfile << "This is a line.\n";
      myfile << "This is another line.\n";

      ap_rputs("wrote to file :)\r\n", r);
      ap_rputs("Unable to open file\r\n", r);

static int myserver_handler(request_rec *r)
    write_something_to_a_file("//home//myfolder//test.txt"); // <-- DOESN'T WORK :(

    return OK;

static void register_hooks(apr_pool_t *pool)
    ap_hook_handler(myserver_handler, NULL, NULL, APR_HOOK_LAST);

module AP_MODULE_DECLARE_DATA   myserver_module =

The output that I get is always:
Unable to open file

What am I missing here?

I'm trying to write to //home//myfolder//test.txt
And I have access to this folder...
Why can't I even create and write to a file?

Thank you for the help!
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James Blond

Joined: 19 Jan 2006
Posts: 7334
Location: Germany, Next to Hamburg

PostPosted: Sat 17 Feb '18 11:33    Post subject: Reply with quote

Use the internal ap_log_error() function from apache itself.
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Joined: 16 Oct 2007
Posts: 2268
Location: Sun Diego, USA

PostPosted: Sun 18 Feb '18 0:03    Post subject: Reply with quote

I cannot compile your module, tried with vc9 on XP & vc14 on Win10 and I get errors in different <c*> headers
depending on the vc version. gcc must be very forgiving.

That said;

Methinks those should be single forward slashes, not double forward slashes.

You also need the request_rec for ap_rputs, in your module r is undefined in write_something_to_a_file().

Why not just use ANSI C's fopen,fprintf,fputs,fclose since the rest of the module and Apache itself is ANSI C.

This compiles and works for me https://apaste.info/mr0T
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