Printf是一个函数而cout是一个变量。

我引用一下:

在高层术语中，主要的区别是类型安全(cstdio 没有它)，性能(大多数iostreams实现都有 比cstdio慢)和可扩展性(iostreams允许 自定义输出目标和用户定义类型的无缝输出)。

Printf是一个函数而cout是一个变量。

我想指出的是，如果你想在c++中使用线程，如果你使用cout，你可以得到一些有趣的结果。

考虑下面的代码:

#include <string>
#include <iostream>
#include <thread>

using namespace std;

void task(int taskNum, string msg) {
    for (int i = 0; i < 5; ++i) {
        cout << "#" << taskNum << ": " << msg << endl;
    }
}

int main() {
    thread t1(task, 1, "AAA");
    thread t2(task, 2, "BBB");
    t1.join();
    t2.join();
    return 0;
}

// g++ ./thread.cpp -o thread.out -ansi -pedantic -pthread -std=c++0x

现在，输出都被打乱了。它也可以产生不同的结果，试着执行几次:

##12::  ABABAB

##12::  ABABAB

##12::  ABABAB

##12::  ABABAB

##12::  ABABAB

你可以使用printf，也可以使用互斥。

#1: AAA
#2: BBB
#1: AAA
#2: BBB
#1: AAA
#2: BBB
#1: AAA
#2: BBB
#1: AAA
#2: BBB

玩得开心!

一个是输出到标准输出的函数。另一个是一个对象，它提供了几个成员函数和输出到stdout的操作符<<的重载。我可以列举更多的不同之处，但我不确定你想要的是什么。

当然，你可以把“something”写得更好一点，以保持维护:

#include <iostream>
#include <cstdlib>

using namespace std;

class Something
{
    public:
        Something(int x, int y, int z) : a(x), b(y), c(z) { }
        int a;
        int b;
        int c;

        friend ostream& operator<<(ostream&, const Something&);

        void print() const { printf("%i, %i, %i\n", a, b, c); }
};

ostream& operator<<(ostream& o, const Something& s)
{
    o << s.a << ", " << s.b << ", " << s.c;
    return o;
}

int main(void)
{
    Something s(3, 2, 1);

    // Output with printf
    s.print(); // Simple as well, isn't it?

    // Output with cout
    cout << s << endl;

    return 0;
}

还有一个cout vs. printf的扩展测试，如果有人想做更多的测试，添加了一个'double'的测试(Visual Studio 2008，可执行文件的发布版本):

#include <stdio.h>
#include <iostream>
#include <ctime>

class TimedSection {
    char const *d_name;
    //timespec d_start;
    clock_t d_start;

    public:
        TimedSection(char const *name) :
            d_name(name)
        {
            //clock_gettime(CLOCK_REALTIME, &d_start);
            d_start = clock();
        }
        ~TimedSection() {
            clock_t end;
            //clock_gettime(CLOCK_REALTIME, &end);
            end = clock();
            double duration = /*1e3 * (end.tv_sec - d_start.tv_sec) +
                              1e-6 * (end.tv_nsec - d_start.tv_nsec);
                              */
                              (double) (end - d_start) / CLOCKS_PER_SEC;

            std::cerr << d_name << '\t' << std::fixed << duration * 1000.0 << " ms\n";
        }
};


int main() {
    const int iters = 1000000;
    char const *text = "01234567890123456789";
    {
        TimedSection s("cout with only endl");
        for (int i = 0; i < iters; ++i)
            std::cout << std::endl;
    }
    {
        TimedSection s("cout with only '\\n'");
        for (int i = 0; i < iters; ++i)
            std::cout << '\n';
    }
    {
        TimedSection s("printf with only '\\n'");
        for (int i = 0; i < iters; ++i)
            printf("\n");
    }
    {
        TimedSection s("cout with string constant and endl");
        for (int i = 0; i < iters; ++i)
            std::cout << "01234567890123456789" << std::endl;
    }
    {
        TimedSection s("cout with string constant and '\\n'");
        for (int i = 0; i < iters; ++i)
            std::cout << "01234567890123456789\n";
    }
    {
        TimedSection s("printf with string constant and '\\n'");
        for (int i = 0; i < iters; ++i)
            printf("01234567890123456789\n");
    }
    {
        TimedSection s("cout with some stuff and endl");
        for (int i = 0; i < iters; ++i)
            std::cout << text << "01234567890123456789" << i << std::endl;
    }
    {
        TimedSection s("cout with some stuff and '\\n'");
        for (int i = 0; i < iters; ++i)
            std::cout << text << "01234567890123456789" << i << '\n';
    }
    {
        TimedSection s("printf with some stuff and '\\n'");
        for (int i = 0; i < iters; ++i)
            printf("%s01234567890123456789%i\n", text, i);
    }
    {
        TimedSection s("cout with formatted double (width & precision once)");
        std::cout << std::fixed << std::scientific << std::right << std::showpoint;
        std::cout.width(8);
        for (int i = 0; i < iters; ++i)
            std::cout << text << 8.315 << i << '\n';
    }
    {
        TimedSection s("cout with formatted double (width & precision on each call)");
        std::cout << std::fixed << std::scientific << std::right << std::showpoint;

        for (int i = 0; i < iters; ++i)
            { std::cout.width(8);
              std::cout.precision(3);
              std::cout << text << 8.315 << i << '\n';
            }
    }
    {
        TimedSection s("printf with formatted double");
        for (int i = 0; i < iters; ++i)
            printf("%8.3f%i\n", 8.315, i);
    }
}

结果是:

cout with only endl    6453.000000 ms
cout with only '\n'    125.000000 ms
printf with only '\n'    156.000000 ms
cout with string constant and endl    6937.000000 ms
cout with string constant and '\n'    1391.000000 ms
printf with string constant and '\n'    3391.000000 ms
cout with some stuff and endl    9672.000000 ms
cout with some stuff and '\n'    7296.000000 ms
printf with some stuff and '\n'    12235.000000 ms
cout with formatted double (width & precision once)    7906.000000 ms
cout with formatted double (width & precision on each call)    9141.000000 ms
printf with formatted double    3312.000000 ms