filled-in text in the "Building" chapter and added a "libcurl with C++"

About this Document

 This document will attempt to describe the general principle and some basic

 approach to consider when programming with libcurl. The text will focus

 approaches to consider when programming with libcurl. The text will focus

 mainly on the C/C++ interface but might apply fairly well on other interfaces

 as well as they usually follow the C one pretty closely.

Building

  There are many different ways to build C programs. This chapter will assume

  a unix-style build process

  Compiling the Program

    Your compiler needs to know where the libcurl headers are

    located. Therefore you must set your compiler's include path to point to

    the directory where you installed them. The 'curl-config' tool can be used

    to get this information:

        $ curl-config --cflags

  Linking the Program with libcurl

    When having compiled the program, you need to link your object files to

    create a single executable. For that to succeed, you need to link with

    libcurl and possibly also with other libraries that libcurl itself depends

    on. Like OpenSSL librararies, but even some standard OS libraries may be

    needed on the command line. To figure out which flags to use, once again

    the 'curl-config' tool comes to the rescue:

        $ curl-config --libs

  SSL or Not

    libcurl can be built and customized in many ways. One of the things that

    varies from different libraries and builds is the support for SSL-based

    transfers, like HTTPS and FTPS. If OpenSSL was detected properly at

    build-time, libcurl will be built with SSL support. To figure out if an

    installed libcurl has been built with SSL support enabled, use

    'curl-config' like this:

        $ curl-config --feature

    And if SSL is supported, the keyword 'SSL' will be written to stdout,

    possibly together with a few other features that can be on and off on

    different libcurls.

Global Preparation

 fast as possible. The callback should return the number of bytes it wrote in

 the buffer. Returning 0 will signal the end of the upload.

libcurl with C++

 There's basicly only one thing to keep in mind when using C++ instead of C

 when interfacing libcurl:

    "The Callbacks Must Be Plain C"

 So if you want a write callback set in libcurl, you should put it within

 'extern'. Similar to this:

     extern "C" {

       size_t write_data(void *ptr, size_t size, size_t nmemb,

                         void *ourpointer)

       {

         /* do what you want with the data */

       }

    }

 This will of course effectively turn the callback code into C. There won't be

 any "this" pointer available etc.

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