Using the Apache Portable Runtime (APR)

The goal of the [http://apr.apache.org APR] project is to provide an API to which software developers may code and be assured of predictable if not identical behaviour regardless of the platform on which their software is built, relieving them of the need to code special-case conditions to work around or take advantage of platform-specific deficiencies or features.

It contains, among other things, the following functionality:

Reading and writing of files
Character set conversion
Network communications using sockets
String management like C++ including natural order management
Filename canonicalization
Memory management
Global lock management
Threads and process management
Dynamic library loading routines
Memory mapped and shared memory
UNIX Password management routines
Time management used for internet type conversions

Missing documentation/introductory material

Unfortunately, the official documentation consists of only a Doxygen generated description of the complete [http://apr.apache.org/docs/apr/1.2/ API] (which is, function by function, quite thorough). There is a tutorial at http://dev.ariel-networks.com/apr/apr-tutorial/, but strangely this is not mentioned on the project web site. Moreover, this tutorial is from 2005.

There seems to be no official tutorial.

For specific questions, it might be helpful to browse the [http://mail-archives.apache.org/mod_mbox/apr-dev/ mailing list archives] (which are not searchable, unfortunately).

APR Hello World

The following is a minimal program that makes use of the APR library:

#include <stdio.h>
#include <apr_general.h>

int main(int argc, const char *argv[])
{
    apr_status_t rv;

    rv = apr_initialize();
    if( rv != APR_SUCCESS ) {
      char errbuf[256];
      apr_strerror(rv, errbuf, sizeof(errbuf));
      puts(errbuf);  /* show the error description */
      return -1;
    }

    printf( "Hello APR world!\n");

    apr_terminate();
    return 0;
}

Compiling under Unix

You have to define the macro LARGEFILE64_SOURCE and link against the apr-1 library::

cc -o try-helloworld-APR try-helloworld-APR.c -D_LARGEFILE64_SOURCE -I/usr/include/apr-1.0/ -lapr-1

FAQ

Q: How can I do getpid() with APR?

A: There is no such concept as a PID on all OSes, so there is no getpid() in APR. See also [http://markmail.org/message/pplgn3urie67htbc#query:+page:1+mid:jjbynsslecwuww3g+state:results this posting].

Q: Which versions of MS-Windows are POSIX compliant? What does this mean for UNIX library function like sleep()? do they exist on windows and have the same behavior? (Are they portable?)

A: ???