CS3157: Advanced Programming Lecture #4 June 6 Shlomo Hershkop - - PowerPoint PPT Presentation

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CS3157: Advanced Programming Lecture #4 June 6 Shlomo Hershkop - - PowerPoint PPT Presentation

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CS3157: Advanced Programming Lecture #4 June 6 Shlomo Hershkop shlomo@cs.columbia.edu 1 Overview Today: Introduction to project 1 Bit of practice Beyond basic types Some Shell Programming 2 Project 1 I will talk

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CS3157: Advanced Programming

Lecture #4 June 6

Shlomo Hershkop shlomo@cs.columbia.edu

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Overview

Today:

Introduction to project 1 Bit of practice Beyond basic types Some Shell Programming

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Project 1

I will talk about this later…. Idea: create a cgi program which will let

you organize your calendar information

Project 1: main website and some

backend

Project 2: backend and search engine ☺

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Making it easier

To make it easier we will be coding parts

  • f the project in class together

Here to answer you questions Here to help you learn Push you to get it done earlier Will still need to work on it on your own etc Remember to have readme + Comments!!

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Step 1

Lets start with simple stuff Goal: Spitting out the front end….. Let me talk about some background stuff

and then we can start programming…

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Some CGI Environmental Variables

  • CONTENT_LENGTH

Length of data passed to cgi via post

  • CONTENT_TYPE
  • QUERY_STRING
  • REMOTE_ADDR

Ip address of client

  • REQUEST_METHOD
  • SCRIPT_NAME
  • SERVER_PORT
  • SERVER_NAME
  • SERVER_SOFTWARE
  • HTTP_FROM
  • HTTP_USER_AGENT
  • HTTP_REFERER
  • HTTP_ACCEPT
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Get vs Post

When you run CGI as get…url is changed

getenv(“QUERY_STRING”)

Post pushes the information via STDIN

getenv(“CONTENT_LENGTH”) getline(… or equivalent..

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Printing out quotes

To print out quotes need \” to show up…

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Lets get started….

Lets write a simple cgi program and test

it…then adopt it for this step 1….

Create a c file “project1.c”

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int main(){ /*cgi so lets print out */ printf( "Content-type: text/html\n\n" ); /* lets check if we are processing inputs */ printf("<html><head><title>Test 1</title></head> <body>"); if( getenv("QUERY_STRING") !=NULL ) { printf("Am processing input"); } else{ printf("Welcome first time<P>"); } printf(“</html>”); } /* end main */

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next

gcc -o project1.cgi.exe project1.c Remember it has to be in cgi-bin Start abyss http://localhost/cgi-bin/project1.cgi.exe

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It should show welcome Now load: http://localhost/cgi-bin/project1.cgi.exe?ss Should see other message…

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next

Lets replace the welcome with a function

call:

Add this to your file:

void showFirstForm();

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if( getenv("QUERY_STRING") !=NULL ) { printf("Am processing input"); }else{ showFirstForm(); }

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Code should look like:

void showFirstForm(){ printf("<form action=\"project1.cgi.exe\" method=\"GET\"> <p>"); printf(" Please enter some text: <input type=\"text\" name=\"string\"></p>"); printf("<input type=\"submit\">"); printf("</form>"); }

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Compile the code Enter some input and press the button What happens ??

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Now change the form to show user

password login

Remember that the password shouldn’t

show up ….intead of text change type to “password” (remember to escape quotes)

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next

Replace the “am processing input with call to processLogin(); For today, want to simply print out the username and password

received

Need to scan through the string and split according to & and = Create variables as needed Use malloc to allocate space once you count…but don’t forget +1 for

slash zero at end

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Code please

man getenv

Will show you what is returned

char *qstring =getenv(“QUERY_STRING”) Remember all variables have to be

created at top

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At this point should have code and

program which when loaded shows a login form, when inputted, shows the input received for GET

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Next change

Allow the user to enter a password and

display it and the user name

Code example

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next

Add functionality for going through a

password file and adding the user and md5 of password to it so that we can later check if the user/password matches…

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Next step

Copy code to project1b.c (on your free time) Adopt for POST

Remember will be reading STDIN NEED TO CHECK INPUT_LENGTH

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Back to c…

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Creating your own types

Equivalent to a class idea in other

programming languages, you can define your own types in c struct name { types }

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example

struct point { int x; int y; }

Usage:

struct point a; a.x = 5; a.y = 10;

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Anonymous structs

Can also create anonymous structs

struct { int x; int y; } a, b;

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Nesting

struct rect { struct point pt1; struct point p2; }

Use:

struct rect largeScreen;

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Making space

Remember in the proceeding examples, simple

types so memory is automatically allocated (in a sense).

struct student {

char * name; int age; } struct student a; a.name = (char*)malloc(sizeof(char)*25)); …

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Use in functions

struct point makePoint(int x, int y) { struct point temp; temp.x = x; temp.y = y; return temp; }

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Operations

Copy Assignments & (addressing) Accessing members How do we compare 2 structs

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Structs and pointers

struct point *example

= (struct point *)malloc(sizeof(struct point));

(*example).x

what does *example.x mean? Shortcut: example->x

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typedef

defining your own types using typedef (for ease

  • f use)

typedef short int smallNumber; typedef unsigned char byte; typedef char String[100]; smallNumber x; byte b; String name;

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enum

define new integer-like types as enumerated types:

enum weather { rain, snow=2, sun=4 }; typedef enum { Red, Orange, Yellow, Green, Blue, Violet } Color;

look like C identifiers (names) are listed (enumerated) in definition treated like integers

start with 0 (unless you set value) can add, subtract — e.g., color + weather cannot print as symbol automatically (you have to write code to

do the translation)

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enum

just fancy syntax for an ordered collection of integer

constants: typedef enum { Red, Orange, Yellow } Color;

is like

#define Red 0 #define Orange 1 #define Yellow 2

here’s another way to define your own boolean:

typedef enum {False, True} boolean;

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Usage

enum Boolean {False, True}; ... enum Boolean shouldWait = True; ... if(shouldWait == False) { .. }

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struct

int main() { struct { int x; char y; float z; } rec; rec.x = 3; rec.y = ’a’; rec.z = 3.1415; printf( "rec = %d %c %f\n",rec.x,rec.y,rec.z ); } // end of main()

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struct

int main() { struct record { int x; char y; float z; }; struct record rec; rec.x = 3; rec.y = ’a’; rec.z = 3.1415; printf( "rec = %d %c %f\n",rec.x,rec.y,rec.z ); } // end of main()

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int main() { typedef struct { int x; char y; float z; } RECORD; RECORD rec; rec.x = 3; rec.y = ’a’; rec.z = 3.1415; printf( "rec = %d %c %f\n",rec.x,rec.y,rec.z ); } // end of main()

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note the use of malloc where “sizeof” takes the struct type as its

argument (not the pointer!) int main() { typedef struct { int x; char y; float z; } RECORD; RECORD *rec = (RECORD *)malloc( sizeof( RECORD )); rec->x = 3; rec->y = ’a’; rec->z = 3.1415; printf( "rec = %d %c %f\n",rec->x,rec->y,rec->z ); } // end of main()

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Important to understand

  • verall size of struct is the sum of the elements, plus padding for alignment

(i.e., how many bytes are allocated)

  • given previous examples: sizeof( rec ) -> 12
  • but, it depends on the size and order of content (e.g., ints need to be

aligned on word boundaries, since size of char is 1 and size of int is 4): struct { char x; int y; char z; } s1; /* x y z */ /* |----|----|----| */ /* sizeof s1 -> 12 */ struct { char x, y; int z; } s2; /* xy z */ /* |----|----| */ /* sizeof s2 -> 8 */

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Reminder

  • pointers to structs are common — especially useful with functions (as

arguments to functions or as function type)

  • two notations for accessing elements: (*sp).field or sp->field
  • (note: *sp.field doesn’t work)

struct xyz { int x, y, z; }; struct xyz s; struct xyz *sp; ... s.x = 1; s.y = 2; s.z = 3; sp = &s; (*sp).z = sp->x + sp->y;

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Arrays of structs

notations for accessing elements: arr[i].field

struct xyz { int x, y, z; }; struct xyz arr[2]; ... arr[0].x = 1; arr[0].y = 2; arr[0].z = 3; arr[1].x = 4; arr[1].y = 5; arr[1].z = 6;

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unions

union like struct:

union u_tag { int ival; float fval; char *sval; } u;

but only one of ival, fval and sval can be used in

an instance of u (think container)

  • verall size is largest of elements
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Example

#define NAME_LEN 40 struct person { char name[NAME_LEN+1]; float height; }; int main( void ) { struct person p; strcpy( p.name,"suzanne" ); p.height = 60; printf( "name = [%s]\n",p.name ); printf( "height = %5.2f inches\n",p.height ); } // end of main()