How You Build a C++ cgi script.

Background

I have been using PHP and perl to create common gateway interface (cgi) scripts for many years. I never had a need to make a cgi script in c/c++ until recently. Some developers are driven to c++ cgi for speed reasons because compiled c++ is much faster than interpreted php or perl. My reason for exploring this now was a little different. I needed to make a script that would run on a standalone linux PC that has a web server but no scripting languages such as php or perl. Therefore, I Googled c++ cgi and was disappointed that I didn't find any examples that show how to create a c++ cgi in the same style often used by php and perl developers. Specifically, my goals for the script format were the following: 1) script must call itself 2) script must accept input via an html form 3) script must be able to parse the data provided in the form.

Materials

c++ compiler
web server with cgi support

Instructions

Copy the script shown below and save it as cpp_cgi_example.cpp.
Copy the Hello_var.c example from http://www.trafficg.org/code_c/hello_var.shtml and save it as getcgivars.c. Delete the main section because you do not need it.

Compile using

sudo g++ -o cpp_cgi_example.cgi cpp_cgi_example.cpp

Copy to your cgi-bin directory using a command like

cp cpp_cgi_example.cgi /usr/lib/cgi-bin/cpp_cgi_example.cgi

Open your page in a browser http://127.0.0.1/cgi-bin/cpp_cgi_example.cgi

More details are provided in the text below.

Sample script

/*************************************************************************/ /** cpp_cgi_example.cpp by HowYouBuildIt.com **/ /** c++ cgi program illustrating how to parse inputs and call itself **/ /** **/ /*************************************************************************/ #include <stdio.h> #include <string.h> #include <stdlib.h> #include <string> using namespace std; #include "getcgivars.c" /* See Hello_var.c at http://www.trafficg.org/code_c/hello_var.shtml */ #define DEBUG false // define all variables to be used in the form(s) string mode; string FirstName; string LastName; string Telephone; string Email; /*************************************************************************/ void DisplayHeader() { printf("Content-type: text/html\n\n"); printf("<html>\n"); printf("<body>\n"); } /*************************************************************************/ void DisplayFooter() { printf("</body>\n"); printf("</html>\n"); } /*************************************************************************/ void Cleanup(char** cgivars) { /* Free anything that needs to be freed */ int i; for (i=0; cgivars[i]; i++) free(cgivars[i]); free(cgivars); } /*************************************************************************/ string httpvar(char** cgivars, string varname) { string output = ""; int i; for (i=0; cgivars[i]; i+= 2) { if (!strcmp(cgivars[i], varname.c_str())) output = cgivars[i+1]; } return output; } /*************************************************************************/ void DisplayForm() { printf ("\n"); printf ("<p align=center><a href='http://www.HowYouBuildIt.com'>How You Build A C++ CGI Script</a></p>"); printf ("<form method='POST' action='%s'>\n", "./cpp_cgi_example.cgi"); printf (" <input name='mode' type=hidden value='update'>\n"); printf ("<table align=center>\n"); printf (" <tr>\n"); printf (" <td>\n"); printf ( "FirstName:\n"); printf (" </td>\n"); printf (" <td>\n"); printf ( "<input name='FirstName' type='text' value='%s'>\n", FirstName.c_str()); printf (" </td>\n"); printf (" </tr>\n"); printf (" <tr>\n"); printf (" <td>\n"); printf ( "LastName:\n"); printf (" </td>\n"); printf (" <td>\n"); printf ( "<input name='LastName' type='text' value='%s'>\n", LastName.c_str()); printf (" </td>\n"); printf (" </tr>\n"); printf (" <tr>\n"); printf (" <td>\n"); printf ( "Telephone:\n"); printf (" </td>\n"); printf (" <td>\n"); printf ( "<input name='Telephone' type='text' value='%s'>\n", Telephone.c_str()); printf (" </td>\n"); printf (" </tr>\n"); printf (" <tr>\n"); printf (" <td>\n"); printf ( "Email:\n"); printf (" </td>\n"); printf (" <td>\n"); printf ( "<input name='Email' type='text' value='%s'>\n", Email.c_str()); printf (" </td>\n"); printf (" </tr>\n"); printf (" <tr>\n"); printf (" <td colspan=2 align=center>\n"); printf ( "<input type=submit value='update'>\n"); printf (" </td>\n"); printf (" </tr>\n"); printf ("</table>\n"); printf (" </form>\n"); } /*************************************************************************/ int main() { char **cgivars; int i; // get each of the form parameters cgivars= getcgivars(); mode = httpvar(cgivars, "mode"); FirstName = httpvar(cgivars, "FirstName"); LastName = httpvar(cgivars, "LastName"); Telephone = httpvar(cgivars, "Telephone"); Email = httpvar(cgivars, "Email"); DisplayHeader(); if (DEBUG) { printf ("mode=%s<dt>\n", mode.c_str()); printf ("FirstName=%s<dt>\n", FirstName.c_str()); printf ("LastName=%s<dt>\n", LastName.c_str()); printf ("Telephone=%s<dt>\n", Telephone.c_str()); printf ("Email=%s<dt>\n", Email.c_str()); } int testmode = 0; if (mode == "update") testmode = 1; switch (testmode) { case 0: // mode == "" DisplayForm(); break; case 1: // mode == "update" printf ("<p align='center'>\n"); printf ("mode=%s<br>\n", mode.c_str()); printf ("FirstName=%s<br>\n", FirstName.c_str()); printf ("LastName=%s<br>\n", LastName.c_str()); printf ("Telephone=%s<br>\n", Telephone.c_str()); printf ("Email=%s<br>\n", Email.c_str()); printf ("</p>\n"); DisplayForm(); break; } DisplayFooter(); Cleanup(cgivars); exit(0); }

Compile

C++ cgi scripts must be compiled to prepare them to be used. Unfortunately, this may present a problem if you do not have a shell/terminal account on the server. These accounts are more rare now due to security precautions but were the norm a decade ago. If you do not have a shell account, you may still be able to compile the script on the same hardware and software if you know what your host is using. Some of the references that I mention in the Bibliography section at the end of this article provide some details on this. Assuming that you have a shell account or your own server, you can compile your script with the command shown below.

sudo g++ -o cpp_cgi_example.cgi cpp_cgi_example.cpp

Copy file to cgi-bin directory

The destination for your cgi script will vary based on the web server that you are using. If you have an ftp account with a major web hosting company, you are often provided a directory "~/cgi-bin" where ~ is a shortcut to your home directory, which is probably something like /home/kevin or /home/howyoubuildit.

cp cpp_cgi_example.cgi /usr/lib/cgi-bin/cpp_cgi_example.cgi

Bibliography

Conclusion

I hope you found this useful. I am a creature of habit and have been using PHP and perl with this format for many years and it took me a little while to figure out how to duplicate that in c++ cgi. The references that I listed were a great help to me in my efforts. In particular, the link at http://www.trafficg.org/code_c/hello_var.shtml was most helpful.