fprintf(cgiOut, "&lt;input type=\"radio\" name=\"age\" "		"value=\"2\"&gt;2\n");	fprintf(cgiOut, "&lt;input type=\"radio\" name=\"age\" "		"value=\"3\" checked&gt;3\n");	fprintf(cgiOut, "&lt;input type=\"radio\" name=\"age\" "		"value=\"4\"&gt;4\n");	fprintf(cgiOut, "&lt;p&gt;Nonexclusive Checkbox Group: "		"Voting for Zero through Four Candidates\n");	fprintf(cgiOut, "&lt;input type=\"checkbox\" name=\"vote\" "		"value=\"A\"&gt;A\n");	fprintf(cgiOut, "&lt;input type=\"checkbox\" name=\"vote\" "		"value=\"B\"&gt;B\n");	fprintf(cgiOut, "&lt;input type=\"checkbox\" name=\"vote\" "		"value=\"C\"&gt;C\n");	fprintf(cgiOut, "&lt;input type=\"checkbox\" name=\"vote\" "		"value=\"D\"&gt;D\n");	fprintf(cgiOut, "&lt;p&gt;File Upload:\n");	fprintf(cgiOut, "&lt;input type=\"file\" name=\"file\" "		"value=\"\"&gt; (Select A Local File)\n");	fprintf(cgiOut, "&lt;p&gt;\n");	fprintf(cgiOut, "&lt;p&gt;Set a Cookie&lt;p&gt;\n");	fprintf(cgiOut, "&lt;input name=\"cname\" "		"value=\"\"&gt; Cookie Name\n");	fprintf(cgiOut, "&lt;input name=\"cvalue\" "		"value=\"\"&gt; Cookie Value&lt;p&gt;\n");	fprintf(cgiOut, "&lt;input type=\"submit\" "		"name=\"testcgic\" value=\"Submit Request\"&gt;\n");	fprintf(cgiOut, "&lt;input type=\"reset\" "		"value=\"Reset Request\"&gt;\n");	fprintf(cgiOut, "&lt;p&gt;Save the CGI Environment&lt;p&gt;\n");	fprintf(cgiOut, "Pressing this button will submit the form, then "		"save the CGI environment so that it can be replayed later "		"by calling cgiReadEnvironment (in a debugger, for "		"instance).&lt;p&gt;\n");	fprintf(cgiOut, "&lt;input type=\"submit\" name=\"saveenvironment\" "		"value=\"Save Environment\"&gt;\n");	fprintf(cgiOut, "&lt;/form&gt;\n");}</pre>Note the use of <code>enctype="multipart/form-data"</code> in the<code>FORM</code> tag. This is absolutely required if the formwill contain file upload fields, as in the above example. Mostbrowsers will not even attempt file uploads without thepresence of this attribute.<h4>Examining CGI environment variables</h4>The CGI standard specifies a number of environment variableswhich are set by the server. However, servers are somewhatunpredictable as to whether these variables will be null orpoint to empty strings when an environment variable is not set.Also, in order to allow the programmer to restore savedCGI environments, the cgic library needs have a way of insulatingthe programmer from the actual environment variables.<p>Instead of calling getenv() to determine the value of avariable such as HTTP_USER_AGENT (the browser software being used),always use the<a href="#variables">cgic copies of the environment variables</a>,which are always valid C strings (they are never null, althoughthey may point to an empty string). For instance, the cgicvariable containing the name of the browser software is<a href="#cgiUserAgent">cgiUserAgent</a>. The referring URL appearsin the variable <a href="#cgiReferrer">cgiReferrer</a>.<h3><a name="images">How can I generate images from my cgic application?</a></h3>cgic can be used in conjunction with the<a href="http://www.boutell.com/gd/">gd graphics library</a>, whichcan produce GIF images on the fly.<p>The following short sample program hints at the possibilities:<pre>#include "cgic.h"#include "gd.h"char *colors[] = {	"red", "green", "blue"};#define colorsTotal 3int cgiMain() {	int colorChosen;	gdImagePtr im;	int r, g, b;	/* Use gd to create an image */	im = gdImageCreate(64, 64);	r = gdImageColorAllocate(im, 255, 0, 0);		g = gdImageColorAllocate(im, 0, 255, 0);		b = gdImageColorAllocate(im, 0, 0, 255);		/* Now use cgic to find out what color the user requested */	<a href="#cgiFormSelectSingle">cgiFormSelectSingle</a>("color", 3, &amp;colorChosen, 0);		/* Now fill with the desired color */	switch(colorChosen) {		case 0:		gdImageFill(im, 32, 32, r);		break;		case 1:		gdImageFill(im, 32, 32, g);		break;		case 2:		gdImageFill(im, 32, 32, b);		break;	}		/* Now output the image. Note the content type! */	cgiHeaderContentType("image/gif");	/* Send the image to cgiOut */	gdImageGif(im, cgiOut);	/* Free the gd image */	gdImageDestroy(im);	return 0;}</pre>Note that this program would need to be linked with both cgic.oand libgd.a. Often programs of this type respond to onecgiPathInfo value or set of form fields by returning an HTML page with an inline image reference that, in turn, generates a GIF image.<h3><a name="debug">Debugging CGI applications: using capture</a></h3>Debugging CGI applications can be a painful task. Since CGI applicationsrun in a special environment created by the web server, it is difficultto execute them in a debugger. However, the cgic library provides a way of capturing "live" CGI environments to a file, and also provides a wayto reload saved environments. <p>The provided program 'capture.c' can be used to capture CGIenvironments. Just change the first line of the cgiMain() functionof capture.c to save the CGI environment to a filename appropriateon your system and type 'make capture'. Then place capture in yourcgi directory and set the form action or other link you want to testto point to it. When the form submission or other link takes place,capture will write the CGI environment active at that time tothe filename you specified in the source. The<a href="#cgiReadEnvironment">cgiReadEnvironment()</a> function can then be invoked on the same filename at the beginning of the cgiMain() function of the application you want to test in order to restore the captured environment.  You can then execute your program in the debugger of your choice,and it should perform exactly as it would have performed hadit been launched by the actual web server, including file uploads,cookies and all other phenomena within the purview of cgic.<p><strong>Important:</strong> Make sure you specify the full path, as thecurrent working directory of a CGI script may not be what youthink it is!<p><strong>Even More Important:</strong> If you call getenv() yourselfin your code, instead of using the provided <a href="#variables">cgic copies of the CGI environment variables</a>, you will<em>not</em> get the values you expect when running witha saved CGI environment. Always use the cgic variables insteadof calling getenv().<h3><a name="functions">cgic function reference</a></h3><dl><br><dt><strong><a name="cgiFormString">cgiFormResultType cgiFormString(	char *name, char *result, int max)</a></strong><br><dd>cgiFormString attempts to retrieve the string sent for the	specified input field. The text will be copied into	the buffer specified by result, up to but not	exceeding max-1 bytes; a terminating null is then	added to complete the string. Regardless of the newline	format submitted by the browser, cgiFormString always	encodes each newline as a single line feed (ascii decimal 10); as	a result the final string may be slightly shorter than indicated	by a call to <a href="#cgiFormStringSpaceNeeded">	cgiFormStringSpaceNeeded</a> but will never be longer.	cgiFormString returns <a href="#cgiFormSuccess">cgiFormSuccess</a> if the string was 	successfully retrieved, 	<a href="#cgiFormTruncated">cgiFormTruncated</a> if the string was	retrieved but was truncated to fit the buffer,	cgiFormEmpty if the string was 	retrieved but was empty, and <a href="#cgiFormNotFound">cgiFormNotFound</a> if no 	such input field was submitted. In the last case, 	an empty string is copied to result. <br><br><dt><strong><a name="cgiFormStringNoNewlines">cgiFormResultType cgiFormStringNoNewlines(	char *name, char *result, int max)</a></strong><br><dd>cgiFormStringNoNewlines() is exactly equivalent to <a href="#cgiFormString">	cgiFormString()</a>, except	that any carriage returns or line feeds that occur in the input	will be stripped out. The use of this function is recommended	for single-line text input fields, as some browsers will submit	carriage returns and line feeds when they should not. <br><br><dt><strong><a name="cgiFormStringSpaceNeeded">cgiFormResultType cgiFormStringSpaceNeeded(	char *name, int *length)</a></strong><br><dd>cgiFormStringSpaceNeeded() is used to determine the length of the input text 	buffer needed to receive the contents of the specified input field. 	This is useful if the programmer wishes to allocate sufficient memory 	for input of arbitrary length. The actual length of the string 	retrieved by a subsequent call to cgiFormString() may be slightly shorter	but will never be longer than *result. On success, cgiFormStringSpaceNeeded() 	sets the value pointed to by length to the number of bytes of data, 	including the terminating null, and returns <a href="#cgiFormSuccess">cgiFormSuccess</a>. If no 	value was submitted for the specified field, cgiFormStringSpaceNeeded sets 	the value pointed to by length to 1 and returns <a href="#cgiFormNotFound">cgiFormNotFound</a>. 1 is	set to ensure space for an empty string (a single null	character) if cgiFormString is called despite the return value.<br><br><dt><strong><a name="cgiFormStringMultiple">cgiFormResultType cgiFormStringMultiple(	char *name, char ***ptrToStringArray)</a></strong><br><dd>cgiFormStringMultiple is useful in the unusual case in which several	input elements in the form have the same name and, for whatever	reason, the programmer does not wish to use the checkbox, radio 	button and selection menu functions provided below. This is	occasionally needed if the programmer cannot know 	in advance what values might appear in a multiple-selection list	or group of checkboxes on a form. The value pointed to	by result will be set to a pointer to an array of strings; the last	entry in the array will be a null pointer.  This array is allocated 	by the CGI library. Important: when done working with the array,	you must call cgiStringArrayFree() with the array pointer as the 	argument.  cgiFormStringMultiple() returns <a href="#cgiFormSuccess">cgiFormSuccess</a> if at least	one occurrence of the name is found, <a href="#cgiFormNotFound">cgiFormNotFound</a>	if no occurrences are found, or cgiFormMemory if not enough	memory is available to allocate the array to be returned.	In all cases except the last, ptrToStringArray is set to point to a 	valid array of strings, with the last element in the array being a 	null pointer; in the out-of-memory case ptrToStringArray is set to 	a null pointer.<br><br><dt><strong><a name="cgiFormEntries">cgiFormResultType cgiFormEntries(	char *name, char ***ptrToStringArray)</a></strong><br><dd>cgiFormEntries is useful when the programmer cannot know the names	of all relevant form fields in advance. The value pointed to	by result will be set to a pointer to an array of strings; the last	entry in the array will be a null pointer.  This array is allocated 	by the CGI library. Important: when done working with the array,	you must call cgiStringArrayFree() with the array pointer as the 	argument. cgiFormEntries() returns <a href="#cgiFormSuccess">cgiFormSuccess</a> except in the event of an out of memory error.	On success, ptrToStringArray is set to point to a 	valid array of strings, with the last element in the array being a 	null pointer; in the out-of-memory case ptrToStringArray is set to 	a null pointer, and 	<a href="#cgiFormOutOfMemory">cgiFormOutOfMemory</a> is returned.<br><br><dt><strong><a name="cgiStringArrayFree">void cgiStringArrayFree(char **stringArray)</a></strong><br><dd>cgiStringArrayFree() is used to free the memory associated with	a string array created by 	<a href="#cgiFormStringMultiple">cgiFormStringMultiple()</a>,	<a href="#cgiFormEntries">cgiFormEntries()</a>, or	<a href="#cgiFormCookies">cgiFormCookies()</a>.<br><br><dt><strong><a name="cgiFormInteger">cgiFormResultType cgiFormInteger(	char *name, int *result, int defaultV)</a></strong><br><dd>cgiFormInteger() attempts to retrieve the integer sent for the	specified input field. The value pointed to by result	will be set to the value submitted. cgiFormInteger() returns 	cgiFormSuccess if the value was successfully retrieved,	cgiFormEmpty if the value submitted is an empty string,	cgiFormBadType if the value submitted is not an integer,	and <a href="#cgiFormNotFound">cgiFormNotFound</a> if no such input field was submitted. 	In the last three cases, the value pointed to by result	is set to the specified default.<br><br><dt><strong><a name="cgiFormIntegerBounded">cgiFormResultType cgiFormIntegerBounded(	char *name, int *result, int min, int max, int defaultV)</a></strong><br><dd>cgiFormIntegerBounded() attempts to retrieve the integer sent for the	specified input field, and constrains the result to be within	the specified bounds. The value pointed to by result	will be set to the value submitted. cgiFormIntegerBounded() returns 	cgiFormSuccess if the value was successfully retrieved,	<a href="#cgiFormConstrained">cgiFormConstrained</a> if the value was out of bounds and result	was adjusted accordingly, <a href="#cgiFormEmpty">cgiFormEmpty</a> if the value submitted is 	an empty string, <a href="#cgiFormBadType">cgiFormBadType</a> if the value submitted is not an 	integer, and <a href="#cgiFormNotFound">cgiFormNotFound</a> if no such input field was submitted. 	In the last three cases, the value pointed to by result	is set to the specified default.<br><br><dt><strong><a name="cgiFormDouble">cgiFormResultType cgiFormDouble(	char *name, double *result, double defaultV)</a></strong><br><dd>cgiFormDouble attempts to retrieve the floating-point value sent for 	the specified input field. The value pointed to by result	will be set to the value submitted. cgiFormDouble returns 	cgiFormSuccess if the value was successfully retrieved,	cgiFormEmpty if the value submitted is an empty string,	cgiFormBadType if the value submitted is not a number,	and <a href="#cgiFormNotFound">cgiFormNotFound</a> if no such input field was submitted. 	In the last three cases, the value pointed to by result	is set to the specified default. <br><br><dt><strong><a name=