Posts tagged c++

Measuring runtime in milliseconds using the C++ 11 chrono library

11 months ago

by Erik Smistad in General

I have been playing around with the new C++ 11 standard. It includes a nice new library called chrono which includes some useful clocks and timers. Below is an example of some macros you can use to time your applications in milliseconds and print out the result. Timing can be turned off by removing the #define TIMING line. Remember to compile the program with C++11 (or C++0x) enabled. For GCC this should be:

g++ main.cpp -std=c++0x

#include <iostream>
#include <chrono>
 
#define TIMING
 
#ifdef TIMING
#define INIT_TIMER auto start = std::chrono::high_resolution_clock::now();
#define START_TIMER  start = std::chrono::high_resolution_clock::now();
#define STOP_TIMER(name)  std::cout << "RUNTIME of " << name << ": " << \
    std::chrono::duration_cast<std::chrono::milliseconds>( \
            std::chrono::high_resolution_clock::now()-start \
    ).count() << " ms " << std::endl; 
#else
#define INIT_TIMER
#define START_TIMER
#define STOP_TIMER(name)
#endif
 
int main() {
    INIT_TIMER
    START_TIMER
    sleep(2);
    STOP_TIMER("sleeping for 2 seconds")
    START_TIMER
    long unsigned int b = 0;
    for(int i = 0; i < 10000000; i++) {
        b += i;
    }
    STOP_TIMER("some long loop")
}

Example output:

RUNTIME of sleeping for 2 seconds: 2000 ms 
RUNTIME of some long loop: 24 ms

Getting started with Google Test (GTest) on Ubuntu

11 months ago

by Erik Smistad in General

Google test is a framework for writing C++ unit tests. In this short post, I explain how to set it up in Ubuntu.

Start by installing the gtest development package:

sudo apt-get install libgtest-dev

Note that this package only install source files. You have to compile the code yourself to create the necessary library files. These source files should be located at /usr/src/gtest. Browse to this folder and use cmake to compile the library:

sudo apt-get install cmake # install cmake
cd /usr/src/gtest
sudo cmake CMakeLists.txt
sudo make
 
# copy or symlink libgtest.a and libgtest_main.a to your /usr/lib folder
sudo cp *.a /usr/lib

Lets say we now want to test the following simple squareRoot function:

// whattotest.cpp
#include <math.h>
 
double squareRoot(const double a) {
    double b = sqrt(a);
    if(b != b) { // nan check
        return -1.0;
    }else{
        return sqrt(a);
    }
}

In the following code, we create two tests that test the function using a simple assertion. There exists many other assertion macros in the framework (see http://code.google.com/p/googletest/wiki/Primer#Assertions). The code contains a small main function that will run all of the tests automatically. Nice and simple!

// tests.cpp
#include "whattotest.cpp"
#include <gtest/gtest.h>
 
TEST(SquareRootTest, PositiveNos) { 
    ASSERT_EQ(6, squareRoot(36.0));
    ASSERT_EQ(18.0, squareRoot(324.0));
    ASSERT_EQ(25.4, squareRoot(645.16));
    ASSERT_EQ(0, squareRoot(0.0));
}
 
TEST(SquareRootTest, NegativeNos) {
    ASSERT_EQ(-1.0, squareRoot(-15.0));
    ASSERT_EQ(-1.0, squareRoot(-0.2));
}
 
int main(int argc, char **argv) {
    testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

The next step is to compile the code. I’ve set up a small CMakeLists.txt file below to compile the tests. This file locates the google test library and links it with the test application. Note that we also have to link to the pthread library or the application won’t compile.

cmake_minimum_required(VERSION 2.6)
 
# Locate GTest
find_package(GTest REQUIRED)
include_directories(${GTEST_INCLUDE_DIRS})
 
# Link runTests with what we want to test and the GTest and pthread library
add_executable(runTests tests.cpp)
target_link_libraries(runTests ${GTEST_LIBRARIES} pthread)