: VLSI n EDA

Problem: Can you figure out what is wrong with following piece of code?

#include <iostream>int main() { int a[5] = {1,2,3,4,5}; for (int i = 4; a[i] >= 0 && i >=0 ; i--) { std::cout<< "ith element of array is "<<a[i]<<std::endl; }}

I would suggest you to try it yourself before scrolling down to see the answer. Its quite interesting,

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Answer : Here, as one can figure out, the intention is to print array elements from end till we don't hit any negative number. In the first look it may seem fine but unfortunately it will end up in ABR (Array Bound Read).

Explanation : After the completion of 5th iteration; i.e. when i = 0, compiler will decrement i; i.e., i will become "-1". It will, then, try to check the condition, which will result in reading a[-1]. Since, array can have indexes only greater than or equal to 0, it will result in an error. Trying to read array elements out of the allowed indexes is termed as Array Bound Read Error. Hence, one should avoid such conditions because it can result into random result. The program can crash anytime. If you are lucky, it may run successfully also. Its all up to your luck. Instead, it should be

for (int i = 5; i>=0 && a[i] >= 0 ; i--) {

i.e. first check index value and then do the array access operation.

Here, with the above solution, one more interesting thing comes up to understand. In AND (&&) operation compiler first evaluates condition1; if it is true, then goes to evaluate condition2; otherwise return false from there only.

For example,

#include <iostream>
int main() {int i = 0;int j= 1;if( ( i == 1) && (++j ==3) ) { std::cout<<"inside if"<<std::endl;}std::cout<<"i is "<<i<<" and j is "<<j<<std::endl;}

Output :

i is 0 and j is 1

Here, as you can see code control will not go into if branch as none of condition is true. since condition1 i==1 is false, compiler will not even check condition2 i.e. value of j will not be incremented.

Internally, compiler might be doing some following kind of transformation to evaluate && operation

bool cond = (i==1); if( cond ) { cond = (++j != 0) ; }if(cond){ std::cout<<"inside if"<<std::endl;}

Also read:

Automatic include of header dependencies in makefile

Library

C++ trivia

Some good reads about process

String class vs dynamically allocated array

Function overloading is a feature inherent in many programming languages including c++. It allows a user to write multiple functions with same name but with different signatures. On calling the function, the version of the function corresponding to the signature will be referred to. Function signature includes function parameters/arguments, but it does not include return type. Function signature may differ in terms of number of parameters or type of parameters. Let us illustrate with the help of a few examples:

Example 1: The two functions below are overloaded, since the return type of arguments differ:

int func(int a,int b);double func(double a,double b);

Example 2: The two functions below are overloaded because they differ in the number of arguments:

int func(int a,int b);int func(int a,int b,int c);

Example 3: The two functions below are not overloaded because they differ only in terms of their return type; the number and type of all the arguments is same.

void func(int a,int b,int c);int func(int a,int b,int c);

Please note that C does not support function overloading because there is no concept of name mangling in C. On the other hand, C++ does support function overloading as name mangling is supported in C++. Name mangling is mangled name of function name and its signature which is used by C++ compiler internally to refer to functions. For instance, in above example 1, mangled name of functions will look something like shown below:

func__int_intfunc__double_double

This way C++ compiler can handle function overloading.

Note : above are not the actual mangled names. Compiler can make some more complicated names. this is just for understanding.

Also read:

Meyer's singleton pattern

Function overloading

Comparison between array, linked list and vector

C function for hexadecimal to decimal conversion

Problem - can you figure out is there something wrong with this code

VLSI UNIVERSE

Interesting programming quiz : Array Bound Read Error

Automatic include of header dependencies in makefile

Library

C++ trivia

Some good reads about process

String class vs dynamically allocated array

Function Overloading

Meyer's singleton pattern

Function overloading

Comparison between array, linked list and vector

C function for hexadecimal to decimal conversion

Problem - can you figure out is there something wrong with this code

Translate

Total Pageviews

Interesting programming quiz : Array Bound Read Error

Automatic include of header dependencies in makefile Library C++ trivia Some good reads about process String class vs dynamically allocated array

Function Overloading

Meyer's singleton pattern Function overloading Comparison between array, linked list and vector C function for hexadecimal to decimal conversion Problem - can you figure out is there something wrong with this code

Translate

Total Pageviews

Automatic include of header dependencies in makefile

Library

C++ trivia

Some good reads about process

String class vs dynamically allocated array

Meyer's singleton pattern

Function overloading

Comparison between array, linked list and vector

C function for hexadecimal to decimal conversion

Problem - can you figure out is there something wrong with this code