OpenMP

参考：https://www.cnblogs.com/ospider/p/5265975.html

omp.cpp

#include <iostream>
#include <omp.h>
#include <array>
using namespace std;
int main(int argc, char **argv)
{  
    array<double, 8> arr = {1.2, 2.4, 3.6, 4.8, 6.0, 7.2, 8.4, 9.6};
    clock_t time_stt = clock();
  
#pragma omp parallel for 
    for (int i = 0; i < arr.size(); i++ )
    {
        std::cout << arr[i] << std::endl;
    }

    cout <<"time use is " << 1000* (clock() - time_stt)/(double)CLOCKS_PER_SEC << "ms " << endl;

    clock_t time_st = clock();
    for (int i = 0; i < arr.size(); i++ )
    {
        std::cout << arr[i] << std::endl;
    }

    cout <<"time use is " << 1000* (clock() - time_st)/(double)CLOCKS_PER_SEC << "ms " << endl;
    clock_t time_s = clock();
#pragma omp parallel for
    for (char i = 'a'; i <= 'z'; i++)
    {
        std::cout << i << std::endl;
    }
    cout <<"time use is " << 1000* (clock() - time_s)/(double)CLOCKS_PER_SEC << "ms " << endl;

    clock_t time_sts = clock();
    for (char i = 'a'; i <= 'z'; i++)
    {
        std::cout << i << std::endl;
    }
    cout <<"time use is " << 1000* (clock() - time_sts)/(double)CLOCKS_PER_SEC << "ms " << endl;
    return 0;
    
}

CMakeLists.txt

cmake_minimum_required(VERSION 2.8)
project(omp)
set(CMAKE_BUILD_TYPE "Release")
set(CMAKE_CXX_FLAGS "-std=c++11")
#-DEIGEN_USE_MKL_ALL")
set(CMAKE_CXX_FLAGS_RELEASE "-O3 -Wall -g")
#find_package(OpenCV REQUIRED)


FIND_PACKAGE( OpenMP REQUIRED) 
if(OPENMP_FOUND) 
message("OPENMP FOUND") 
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}") 
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}") 
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}") 
endif()


#include_directories( ${OpenCV_INCLUDE_DIRS} ${catkin_INCLUDE_DIRS})


add_executable(omp omp.cpp)


target_link_libraries(omp ${OpenMP_LIBS})

执行结果：

nzp@nzp-T470:~/桌面/并行/omp_test/build$ ./omp 
8.4
3.69.6
1.2
62.4

7.2

4.8
time use is 4.484ms 
1.2
2.4
3.6
4.8
6
7.2
8.4
9.6
time use is 0.014ms 
uo

ph
aq

b
c
d
vi

r
s
t
e
w
x
y
z

f
g
j
k
l
m
n
time use is 2.309ms 
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
time use is 0.062ms 

 

并行并不比串快。