The debugger

The debugger • Some programs may compile correctly, yet not produce the desirable results. • These programs are valid and correct C programs, yet not the programs we meant to write! • The debugger can be used to follow the program step by step and may help detecting bugs in an already compiled program.

The debugger’s common features • Setting breakpoints (a point where the execution stops): bring the cursor to desired line and press the palm icon or F9. A dark red dot appears near the line. • Executing a debugged run: Build->start debug->go or F5. The program will run and stop at the first breakpoint.

The debugger’s common features (cont.) • Stopping at a specific line: Bringing the cursor to the line and press ctrl+F10, or Build->start debug->go to cursor. The program will stop at that point. • Stepping to the next line – F10. • Entering a function – F11. • Seeing variable values – quickwatch and/or debug window at the bottom. • The yellow arrow indicates our whereabouts at any given moment.

Examples factorial_func.c getchar.c

Buggy examples pi_bad.c exp_bad.c

Arrays • A block of many variables of the same type • Array can be declared for any type • E.g. int A[10] is an array of 10 integers. • Examples: • list of students’ marks • series of numbers entered by user • vectors • matrices

Arrays in Memory • Sequence of variables of specified type • The array variable itself holds the address in memory of beginning of sequence • Example: double S[10]; • The k-th element of array A is specified by A[k-1] (0 based) … 0 1 2 3 4 5 6 7 8 9 … S

Example - reverse #include <stdio.h> int main(void) { int i, A[10]; printf("please enter 10 numbers:\n"); for(i=0; i<10; i++) scanf("%d",&A[i]); printf("numbers in reversed order:\n"); for(i=9; i>=0; i--) printf("%d\n",A[i]); }

Define • Magic Numbers (like 10 in the last example) in the program convey little information to the reader • Hard to change in a systematic way • #define defines a symbolic name • During preprocessing phase, symbolic names are replaced by the replacement text

Reverse with #define /* get 10 integers from the user and printing them in reversed order*/ #include <stdio.h> #define NUM 10 int main(void) { int i; int A[NUM]; printf(“Please enter %d numbers:\n",NUM); for(i=0; i<NUM; i++) scanf("%d",&A[i]); printf("numbers in reversed order:\n"); for(i=NUM-1; i>=0; i--) printf("%d\n",A[i]); }

Initialization • Like in the case of regular variables, we can initialize the array during declaration. • the number of initializers cannot be more than the number of elements in the array • but it can be less • in which case, the remaining elements are initialized to 0 • if you like, the array size can be inferred from the number of initializers • by leaving the square brackets empty • so these are identical declarations : int array1 [8] = {2, 4, 6, 8, 10, 12, 14, 16}; int array2 [] = {2, 4, 6, 8, 10, 12, 14, 16};

Example Sort.c

A[0] A[1] A[2] Sort – step by step 4 8 2 min_index ---- i j tmp #include <stdio.h> #define SIZE 3 int main(void) { int A[SIZE] = {4,8,2}; int min_index; int i,j,tmp; ---- ---- ----

A[0] A[1] A[2] Sort – step by step 4 8 2 min_index ---- i j tmp for(i=0; i<SIZE-1; i++) { min_index=i; for(j=i+1; j<SIZE; j++) min_index=(A[min_index]>A[j] ? j : min_index); tmp=A[i]; A[i]=A[min_index]; A[min_index]=tmp; } 0 ---- ----

A[0] A[1] A[2] Sort – step by step 4 8 2 min_index 0 i j tmp for(i=0; i<SIZE-1; i++) { min_index=i; for(j=i+1; j<SIZE; j++) min_index=(A[min_index]>A[j] ? j : min_index); tmp=A[i]; A[i]=A[min_index]; A[min_index]=tmp; } 0 ---- ----

A[0] A[1] A[2] Sort – step by step 4 8 2 min_index 0 i j tmp for(i=0; i<SIZE-1; i++) { min_index=i; for(j=i+1; j<SIZE; j++) min_index=(A[min_index]>A[j] ? j : min_index); tmp=A[i]; A[i]=A[min_index]; A[min_index]=tmp; } 0 1 ----

A[0] A[1] A[2] Sort – step by step 4 8 2 min_index 2 i j tmp for(i=0; i<SIZE-1; i++) { min_index=i; for(j=i+1; j<SIZE; j++) min_index=(A[min_index]>A[j] ? j : min_index); tmp=A[i]; A[i]=A[min_index]; A[min_index]=tmp; } 0 3 4

Exercise Write a program that gets an input line from the user (ends with ‘\n’) and displays the number of times each letter appears in it. Example: For the input line - hello, world! The output should be: d - 1 e – 1 h – 1 l – 2 o – 2 w - 1 Assume that the input is all in lower-case.

Solution letter_count.c

Passing arrays to functions • Functions can accept arrays as arguments • Usually the array’s size also needs to be passed (why?) • For example - int CalcSum(int arr[], int size); • Within the function, arr is accessed in the usual way • Example – calc_sum.c

Passing arrays to functions • Arrays can be passed to functions and have their values changed from within the function! • Unlike regular variables • This is possible because an array variable is actually an address. • Example – vec_mul.c

Exercise • Implement a function that accepts two integer arrays and returns 1 if they are equal, 0 otherwise • Write a program that accepts two arrays of integers from the user and checks for equality • (assume their size is 10)

Solution • compare_arrays.c

Two Dimensional Arrays • We sometimes want to keep an inherent Two-Dimensional structure of data • Example: We can define a two-dimensional 3x3 matrix bydouble A[3][3];

Two Dimensional Arrays • Array of arrays: int A[2][3] = { {1, 2, 3}, {4, 5, 6} }; • Means an array of 2 integer arrays, each of length 3. • Access: j-th element of the i-th array is A[i][j]

Two Dimensional Arrays • When passing a two-dimensional array to a function, it is necessary to indicate the size of the second dimension in the function header • But this does not mean the array’s size needn’t be passed as well • Same is true when initializing the array int func(int[][4] arr);double B[][2] = {{1,2}, {2,3}, {3,4}};

Example mat_add.c

Exercise • Write a program that defines 3 matrices A,B,C of size 3x3 with float elements; initialize the first two matrices (A and B) • Compute the matrix multiplication of A and B and store it in C (i.e. C = A*B) • Matrix Multiplication: • Print all the matrices on the screen

Solution mat_mul.c

The debugger

The debugger

Presentation Transcript

Rr0d: The Rasta Ring0 Debugger

iSeries GUI Debugger

Helikaon Linux Debugger:

Debugger

Colleague Studio Debugger

TotalView Debugger

Subversion/Eclipse/Debugger

The Spark Debugger

Spark Debugger

Rr0d: The Rasta Ring0 Debugger

The Perl Debugger

Lab 1 – Learning the Debugger

Debugger?

Debugger

Exploring Objects with the Debugger

The Debugger and Inspector

Compiler and Debugger

Debugger