COP 3530 Spring2012 Data Structures & Algorithms

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COP 3530 Spring2012 Data Structures & Algorithms. Discussion Session Week 2. Outline. TA contact g++ makefile debug. About me. TA contact. Tao Li PhD student at CISE tali@cise.ufl.edu http://www.cise.ufl.edu/~tali Office Hour This Week: Thursday 9 th period at E309.

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### COP 3530 Spring2012Data Structures & Algorithms

Discussion Session Week 2

Outline
• TA contact
• g++
• makefile
• debug
TA contact

Tao Li

PhD student at CISE

tali@cise.ufl.edu

http://www.cise.ufl.edu/~tali

Office Hour This Week:

Thursday 9th period at E309

Separate code

#ifndef _my_stack#define _my_stackint add(int x, int y); // function prototype for add.h

#endif

.cpp file

int add(int x, int y){ return x + y;}

Because header files can include other header files, it is possible to end up in the situation where a header file gets included multiple times.

Compilation: g++
• Compiling, in which C++ code is translated into assembly;
• Assembling, in which assembly is translated into machine language; and
• Linking, in which calls to functions outside the main file are linked to their definitions.

////////////////////////////////////////////////

g++ -c MyStack.cpp

g++  -c main.cpp

g++  -o stack main.oMyStack.o

or

////////////////////////////////////////////////

g++  -o stack main.cpp MyStack.cpp

-o program_name         // compiling and linking to generate program_name, default "a.out"

-c                                // compiling but no linking-g                                // for debugging, but runs slow

make and makefile

make is a system designed to create programs from large source code trees and to maximize the efficiency of doing so. To that effect, make uses a file in each directory called a Makefile. This file contains instructions for make on how to build your program and when.

target: dependencies<tab>instructions<enter>

example

Note: Build several independent targets in order, below is

sample makefile

==========================================================

all: target1 target2 target3

target1: dependencies

<tab>instructions<enter>

target2: ...

Stack

A stack is a last in, first out (LIFO)  data structure

Main.cpp & Input file

if(x == 1) {

fscanf(fp1, “ %d”, &y);

myStack.Push(y);

} else {

myStack.Top(y);

printf(“%d\n”, y);

myStack.Pop();

}

1 1

1 2

1 3

1 4

1 5

0

0

0

0

Run

./program_name

For example:

./stack

GNU debugger -- gdb

A symbolic debugger is a program that aids programmers in finding logical errors, by allowing them to execute their program in a controlled manner.

• Enable symbol table
• Debug the program

g++ -g -o stack stack.cpp

gdb stack

Use gdb

Starting Execution of Program

(gdb) run (or r)

Quitting gdb

(gdb) quit (or q or Ctrl-D)

Resuming Execution at a BreakpointOnce you have suspended execution at a particular statement, you can resume execution in several ways:

continue (or c)  Resumes execution and continues until the next breakpoint or until execution is completed.

next (or n)  next will execute a function in the current statement in its entirety.

Setting Breakpoints & Print

Setting a breakpoint permits you to mark a particular line in your program (called a breakpoint) so that when execution reaches that line, program execution will be suspended, allowing you to enter a gdb command.

break function: Set a breakpoint at entry to function function.

break filename:linenum :Set a breakpoint at line linenum in source file filename.

print expression (or p expression)Displays the value of the expression (usually a variable) once → at the current point of execution.

Example: tst.cpp

1. #include “stdio.h”

2. int summation(int n) {

3. int sum = 0, i;

4. for(i = 1; i<n; i++) {

• sum += i;
• }

7. return sum;

8. }

9. int main() {

10. printf(“Summation is %d\n”, summation(100));

11. return 0;

12. }

Example

g++ tst.cpp -o tst

./tst

Output:

Summation is 4950

Actually:

1+2+…+100 = (1+100) * 100 / 2 = 5050

Where is the bug?

Tip: Reduce the input size

Change

printf(“Summation is %d\n”, summation(100));

To:

printf(“Summation is %d\n”, summation(5));

Expected result: 1+2+3+4+5 = 15

g++ tst.cpp -o tst

./tst

Output:

Summation is 10

gdb

Compile: g++ -g tst.cpp -o tst

Run gdb: gdbtst

List code: l

Breakpoint: break 5

Run to bkpnt: r

Next step： n

Print value: p (variable)

Finish: finish

Quit: q

The power of PRINTF

printf(“i=%d, sum=%d\n”, i, sum);

Output:

i = 1, sum = 1

i = 2, sum = 3

i = 3, sum = 6

i = 4, sum = 10

Summation is 10