Yolinux.com Tutorial

C++ CGI library GNU CgiCc and Linux

Web CGI programs can be written in any language which can process standard input (stdin), environment variables and write to standard output (stdout). The web server will interact with all CGI programs using the "Common Gateway Interface" (CGI) standard as set by RFC 3875. This capability is possessed by most modern computer programming and scripting languages, including C++. The Advantage of C++ vs scripting languages is its' speed and its' interface with the Operating System using "C" system calls.

This tutorial covers the basics of using the GNU CgiCc C++ library with Apache on Linux. The CgiCc library supports HTML forms and CGI GET and POST functions, HTTP cookies and file uploads. This class library relies heavily on STL (Standard Template Libraries) and String classes. See:

Related YoLinux Tutorials:

°Bash shell CGI

°CGI scripting languages

°Java and Apache Tomcat

°Apache Web Server Configuration

°Software development tools

°Advanced VI

°Emacs and C/C++

°C++ Info, links

°MS/Visual C++ Practices

°C++ Memory corruption and leaks

°C++ String Class

°C++ Templates

°C++ STL vector, list

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°Fork and Exec

°GDK Threads

°YoLinux Tutorials Index




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Download, Installation, Configuration:

Download: ftp://ftp.gnu.org/gnu/cgicc/

Unpack: tar xzf cgicc-X.X.X.tar.gz

Build Libraries:

  • cd cgicc-X.X.X/
  • ./configure --prefix=/usr (Default or /opt. Make sure you have write priviges to the directory.)
    If compiling to create a 32 bit library on a 64 bit Athelon:
    CXXFLAGS="-m32" CFLAGS="-m32" LDFLAGS="-m32"
    If installed in /opt then you will need to include:
    • Include path defined in the compile statement: -I/opt/include
    • Link command reference: -L/opt/lib
      or use LD_RUN_PATH or /etc/ld.so.conf
    Installing into /usr may eliminate the configuration headaches but will not isolate your development libraries from the distribution libraries.
  • make install
[Potential Pitfall]: If cgicc does not build on your version and flavor of Linux, try a different version. When using older versions of Linux, try an older and contemporary version of cgicc.

The build and installation will create and install include files, documentation and libraries:

  • Libraries:
             /usr/lib/libcgicc.a
             libcgicc.la
             libcgicc.so              (softlink to libcgicc.so.1.3.0)
             libcgicc.so.1            (softlink to libcgicc.so.1.3.0)
             libcgicc.so.1.3.0
            
  • Include files: /usr/include/cgicc/...
  • Documentation: /usr/doc/cgicc-X.X.X/index.html
    Also available at http://www.gnu.org/software/cgicc/doc/


Example:

The Web Page:

Test CGIcc form

Value 1 :

Value 2 :

Value 3 : Button1 Button2

HTML Form Source:

<html>
<head><title>Test CGIcc form</title></head>
<body bgcolor="#cccccc" text="#000000">
<h2>Test CGIcc form</h2>
<p>
<form method="post" action="/cgi-bin/testcgi">
Value 1 :
<input type="text" name="value1">
<p>
Value 2 :
<select name="value2">
   <option value="option1">Option 1
   <option value="option2">Option 2
   <option value="option3">Option 3
</select>
<P>
Value 3 :
<input type="radio" name="value3" value="button1" checked="checked">Button1
<input type="radio" name="value3" value="button2">Button2

<input type="hidden" name="value4" value="data4">
<p>
<input type="submit" value="Submit">
</form>
</body>
</html>

C++ CGI Source:

#include <iostream>
#include <vector>
#include <string>

#include "cgicc/CgiDefs.h"
#include "cgicc/Cgicc.h"
#include "cgicc/HTTPHTMLHeader.h"
#include "cgicc/HTMLClasses.h"

#include <stdio.h>
#include <stdlib.h>

using namespace std;
using namespace cgicc;     // Or reference as cgicc::Cgicc formData; below in object instantiation.

int main(int argc, char **argv)
{
    try {
       Cgicc formData;

       // Send HTTP header: Content-type: text/html
       cout << HTTPHTMLHeader() << endl;

       // Print: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd">
       cout << HTMLDoctype(HTMLDoctype::eStrict) << endl;

       // Print: <html lang="en" dir="LTR">
       cout << html().set("lang", "EN").set("dir", "LTR") << endl;

       // Set up the HTML document
       cout << html() << head() << title("Cgicc example") << head() << endl;
       cout << body().set("bgcolor","#cccccc").set("text","#000000").set("link","#0000ff").set("vlink","#000080") << endl;

       cout << h1("This is a demonstration of the GNU CgiCC library") << endl;

       form_iterator fvalue1 = formData.getElement("value1");
       if( !fvalue1->isEmpty() && fvalue1 != (*formData).end()) {
          cout << "Value1: " << **fvalue1 << endl;
       }
       else
          cout << "No text entered for value1" << endl;

       cout << p();

       form_iterator fvalue2 = formData.getElement("value2");
       if( !fvalue2->isEmpty() && fvalue2 != (*formData).end()) {
          // Note this is just a different way to access the string class.
          // See the YoLinux GNU string class tutorial.
          cout << "Value2: " << (**fvalue2).c_str() << endl;
       }

       cout << p();

       form_iterator fvalue3 = formData.getElement("value3");
       if( !fvalue3->isEmpty() && fvalue3 != (*formData).end()) {
          cout << "Value3: " << **fvalue3 << endl;
       }

       cout << p();

       form_iterator fvalue4 = formData.getElement("value4");
       if( !fvalue4->isEmpty() && fvalue4 != (*formData).end()) {
          cout << "Value4: " << **fvalue4 << endl;
       }

       // Close the HTML document
       cout << body() << html();
    }
    catch(exception& e) {
       // handle any errors here.
       cout << "ERROR!!" << endl;
    }
    return 0;   // To avoid Apache errors.
}

Compile:

  • Compile and static link: (size: 1063688)
    • If installed in /opt/: g++ -o testcgi -I/opt/include testcgi.cpp /opt/lib/libcgicc.a
    • If installed in /usr/: g++ -o testcgi testcgi.cpp /usr/lib/libcgicc.a
  • Dynamic Link (at run time): (size: 48465)
    • If installed in /opt/: g++ -o testcgi -I/opt/include testcgi.cpp -L/opt/lib -lcgicc
    • If installed in /usr/: g++ -o testcgi testcgi.cpp -lcgicc

Run:

The following paths are for a Red Hat 7.x installation.
  1. Place web page in: /var/www/html/testcgi.html
  2. Place cgi in: /var/www/cgi-bin/testcgi
  3. Start Apache: service httpd start
  4. Test: http://localhost/testcgi.html


Debugging:

Debugging a "POST" method CGI:

  • Print environment for transaction:
    Code snipet to include in cgicc CGI program:
    // Function declaration
    void dumpEnvironment(const CgiEnvironment& env);
    ...
    
        const CgiEnvironment& env = cgi.getEnvironment();
        
        cout << env.getRequestMethod() << endl; 
        ...     env.getPathInfo()        ...
        ...     env.getPathTranslated()
                env.getReferrer()
                env.getContentLength()
                env.getPostData() 
        ... 
        
    Also: env.getRequestMethod(), env.getPathInfo(), env.getPathTranslated(), env.getReferrer(), env.getContentLength(), env.getPostData(), env.getRemoteHost(), env.getRemoteAddr(), env.getAuthType(), env.getRemoteUser(), env.getRemoteIdent(), env.getContentType(), env.getAccept(), env.getUserAgent(), env.getServerSoftware(), env.getServerName(), env.getGatewayInterface(), env.getServerProtocol(), env.getServerPort(), env.usingHTTPS(), env.getRedirectRequest(), env.getRedirectURL(), env.getRedirectStatus(), env.getCookies(), env.getQueryString(), env.getScriptName().

  • Set environment variables: . debug-env
    File: debug-env
    export HTTP_USER_AGENT="Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.7.3) Gecko/20041020"
    export SERVER_PORT=80
    export HTTP_HOST=localhost
    export DOCUMENT_ROOT="/var/www/html"
    export HTTP_ACCEPT_CHARSET="iso-8859-1,*,utf-8"
    export SCRIPT_FILENAME="/var/www/cgi-bin/env.sh"
    export REQUEST_URI="/cgi-bin/env.sh"
    export SCRIPT_NAME="/cgi-bin/program.cgi"
    export HTTP_REFERRER="http://localhost/web-page.html"
    export HTTP_CONNECTION=Keep-Alive""
    export REMOTE_PORT=32984
    export PATH="/sbin:/usr/sbin:/bin:/usr/bin:/usr/X11R6/bin"
    export PWD="/var/www/cgi-bin"
    export SERVER_ADMIN="root@localhost"
    export HTTP_ACCEPT_LANGUAGE=en
    export HTTP_ACCEPT='text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5'
    export REMOTE_ADDR='127.0.0.1'
    export SHLVL=1
    export SERVER_NAME=localhost
    export SERVER_SOFTWARE='Apache/2.0.52 (Fedora)'
    export QUERY_STRING=
    export SERVER_ADDR='127.0.0.1'
    export GATEWAY_INTERFACE='CGI/1.1'
    export SERVER_PROTOCOL='HTTP/1.1'
    export HTTP_ACCEPT_ENCODING=gzip
    export REQUEST_METHOD=POST
    export CONTENT_LENGTH=47
    export CONTENT_TYPE='application/x-www-form-urlencoded'
    export POST_DATA='formval1=VALUE1&formval2=VALUE2&formval3=VALUE3'

  • Create file for (standard input) stdin: echo $POST_DATA > debug-stdin

  • Run in dbx:
    • dbx program.cgi
    • break ##### (Set breakpoints)
    • run < debug-stdin
    OR
    If not debugging, just run: echo $POST_DATA | ./program.cgi


Links:


Books:

CGI: Internet Programming in C++ and C
by Mark Felton
ISBN #0137123582, Prentice Hall

Amazon.com
C++ How to Program
by Harvey M. Deitel, Paul J. Deitel
ISBN #0131857576, Prentice Hall

Fifth edition. The first edition of this book (and Professor Sheely at UTA) taught me to program C++. It is complete and covers all the nuances of the C++ language. It also has good code examples. Good for both learning and reference.

Amazon.com
The C++ Standard Library: A Tutorial Reference
Nicolai M. Josuttis
ISBN #0201379260, Addison Wesley Longman

This book is the only book I have seen which covers string classes as implemented by current Linux distributions. It offers extensive coverage of the C++ string classes as well as fairly complete coverage of the C++ Standard Template Library (STL).

Amazon.com

Copyright © 2002 - 2009 by Greg Ippolito