Visual Studio中的C++运行结构

Question

我在同一个项目中有两个文件，分别是f1.cpp和f2.cpp，用于解决算法中相同的“连通性问题”。在 visual studio 中，我将它们放入源文件中。源文件中的另一个文件是 pch.cpp。项目名称也是 f1。

f1.cpp的代码是，

#include "pch.h"
#include <iostream>

using namespace std;

static const int N = 10000;

int main()
{
    int i, p, q, id[N];
    for (i = 0; i < N; i++) id[i] = i;
    while (cin >> p >> q) {
        int t = id[p];
        if (t == id[q]) continue;
        for (i = 0; i < N; i++)
            // this is for union 
            if (id[i] == t) id[i] = id[q];
        cout << " " << p << " " << q << endl;
    }
    std::cout << "Hello World!\n"; 
    return 0;
}

f2.cpp 是，

#include <iostream>
#include "pch.h"

using namespace std;

static const int N = 10000;
int main() {
    int i, j, p, q, id[N], sz[N];
    for (i = 0; i < N; i++) { id[i] = i, sz[i] = 1; }
    while (cin >> p >> q) {
        for (i = p; i != id[i]; i = id[i]);
        for (j = q; j != id[j]; j = id[j]);
        if (i == j) continue;
        if (sz[i] < sz[j]) {
            id[i] = j; sz[j] += sz[i];
        }
        else {
            id[j] = i; sz[i] += sz[j];
        }
        cout << " " << p << " " << q << endl;
    }
}

虽然我很确定这两个代码，如果独立运行，是没有错误的。但是当它们一起出现在源文件中时，当我运行 f2.cpp 时，会出现错误

C2065 'cin': undeclared identifier connectivity problem
C2065 'cout': undeclared identifier connectivity problem
C2065 'endl': undeclared identifier connectivity problem

My question is why the error like this happens ? 
Do I have to open a new project in visual studio for editing different solutions on same problems ? 

Answer 1

就像我之前指出的那样，如果同时运行多个源文件，链接器将生成两个 main() 方法，这将导致编译器错误，因为您只能有一个 主()...

记住程序只能指向一个main()函数...

但是，您可以在代码中使用#define:

#include "pch.h"
#include <iostream>

using namespace std;

static const int N = 10000;

// Running the first project...
#define F_PROJ

// Psuedo main for first project...
int first_main()
{
    int i, p, q, id[N];
    for (i = 0; i < N; i++) id[i] = i;
    while (cin >> p >> q) {
        int t = id[p];
        if (t == id[q]) continue;
        for (i = 0; i < N; i++)
            // this is for union 
            if (id[i] == t) id[i] = id[q];
        cout << " " << p << " " << q << endl;
    }
    std::cout << "Hello World!\n";
    return 0;
}

// Psuedo main for second project...
int second_main()
{
    int i, j, p, q, id[N], sz[N];
    for (i = 0; i < N; i++) { id[i] = i, sz[i] = 1; }
    while (cin >> p >> q) {
        for (i = p; i != id[i]; i = id[i]);
        for (j = q; j != id[j]; j = id[j]);
        if (i == j) continue;
        if (sz[i] < sz[j]) {
            id[i] = j; sz[j] += sz[i];
        }
        else {
            id[j] = i; sz[i] += sz[j];
        }
        cout << " " << p << " " << q << endl;
    }
    return 0;
}

int main()
{
#ifdef F_PROJ
    first_main();
#elif defined(S_PROJ)
    second_main();
#endif
}

只需分别点#define F_PROJ或#define S_PROJ...