為什麼要進行CGI程式設計? 

GET表單的處理 

<FORM ACTION="/cgi-bin/multi.cgi"> 

	<P>請在下面填入乘數和被乘數，按下確定後可以看到結果。 </p>

<INPUT NAME="m" SIZE="5"> 

<INPUT NAME="n" SIZE="5"></BR> 

<INPUT TYPE="SUBMIT" VALUE="確定"> 

</FORM> 

　　 我們要實現的功能很簡單，就是把表單中輸入的數值乘起來，然後輸出結果。其實這個功能完全可以用JavaScript來實現，但為了讓程式儘量的簡單易懂，我還是選擇了這個小小的乘法來作為示例。 

#include <stdio.h>  
#include <stdlib.h>  
  
int main(void) {  
    char *data;  
    long m;  
    long n;  
      
    printf("%s%c%c\n", "Content-Type:text/html;charset=gb2312", 13, 10);  
    printf("<TITLE>Result of multiplication</TITLE>\n");  
    printf("<H3>Result of multiplication</H3>\n");  
    data = getenv("QUERY_STRING");  
    if (data == NULL) {  
        printf("<P>ERROR！Data is not input or data transfer has problem</P>\n");  
    }  
    else if(sscanf(data,"m=%ld&n=%ld", &m, &n) != 2) {  
        printf("<P>ERROR！The input data is invalid, you must input digit number</P>\n");  
    }  
    else {  
        printf("<P>%ld and %ld equals: %ld.\n", m, n, m*n);  
    }  
  
    return 0;  
}  

POST表單處理 

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


#define MAXLEN 80
/* 4 for field name "data", 1 for "=" */
#define EXTRA 5
/* 1 for added line break, 1 for trailing NUL */
#define MAXINPUT MAXLEN+EXTRA+2
#define DATAFILE "./data.txt"
 
void unencode(char *src, char *last, char *dest) {
    for(; src != last; src++, dest++)
        if (*src == '+') {
            *dest = ' ';
        }
        else if(*src == '%') {
            int code;
            if (sscanf(src+1, "%2x", &code) != 1) {
                code = '?';
            }
            *dest = code;
            src +=2;
        }     
        else {
            *dest = *src;
        }
    *dest = '\n';
    *++dest = '\0';
}
 
int main(void) {
    char *lenstr;
    char input[MAXINPUT];
    char data[MAXINPUT];
    long len;


    printf("%s%c%c\n", "Content-Type:text/html;charset=iso-8859-1",13,10);
    printf("<TITLE>Response</TITLE>\n");

    lenstr = getenv("CONTENT_LENGTH");
    if (lenstr == NULL || sscanf(lenstr,"%ld",&len) != 1 || len > MAXLEN) {
        printf("<P>Error in invocation - wrong FORM probably.\n");
    }
    else {
        printf("<p>CONTENT_LENGTH is %ld %d.</p>\n", len, atoi(lenstr));
        // fgets(input, len+1, stdin);
        fgets(input, len+1, stdin);
        unencode(input+EXTRA, input+len, data);


        FILE *fp;
        fp = fopen(DATAFILE, "a+");
        if(fp == NULL) {
            printf("<p>Sorry, cannot store your data.</p>");
        }
        else {
            printf("<p>Your data is: %s.</p>\n",  data);
            fputs(data, fp);
        }
        fclose(fp);


        printf("<p>Thank you! The following contribution of yours has been stored:</br></p>%s\n",data);
    }


    return 0;
}

<FORM ACTION="/cgi-bin/collect.cgi" METHOD="POST"> 

	<P>請輸入您的留言（最多80個字元）：</BR><INPUT NAME="data" SIZE="60" MAXLENGTH="80"></BR></p>

<INPUT TYPE="SUBMIT" VALUE="確定"> 

</FORM>

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


#define DATAFILE "data.txt"


int main(void) {
    FILE *f = fopen(DATAFILE,"r");
    if(f == NULL) {
        printf("%s%c%c\n", "Content-Type:text/html;charset=iso-8859-1", 13, 10);
        printf("<TITLE>Failure</TITLE>\n");
        printf("<P><EM>Unable to open data file, sorry!</EM></p>");
    }
    else {
        printf("%s%c%c\n", "Content-Type:text/plain;charset=iso-8859-1", 13, 10);
        int ch;
        while ( (ch=getc(f)) != EOF) {
            putchar(ch);
        }
        fclose(f);
    }


    return 0;
}

<form action="http://127.0.0.1/cgi-bin/view_data.cgi">
    <p>Click the button to view the text content in data.txt</p>
<div><input type="submit" value="View"></div>
</form>