Question

C：\ Users \ George \ Desktop \ linear_equation_calc \ main.cpp ||在功能中 'int main（int，const char **）'：| C：\ Users \用户乔治\桌面\ linear_equation_calc \ main.cpp中| 101 |错误： 'calcparallelplugin'未在此范围中声明 || ===构建完成：1个错误，0个警告=== |

这是我不断得到的错误。我明白什么声明的意思，但我真的不明白我应该如何声明它使用calcparallelplugin（）来链接另一个.cpp文件。我知道它的标准做法不是单独的.cpp文件而不是标题。有人用非常简单的术语解释，我现在和s ***一样厚，

#include <iostream>
#include <string.h>

using namespace std;

// Function includes
// I try to keep them in the order they appear in the
// output below for organization purposes
#include "calc.m.xy12plugin.cpp"
#include "calc.b.xymplugin.cpp"
#include "calc.m.xybplugin.cpp"
#include "calc.point.xymplugin.cpp"
#include "calc.parallelplugin.cpp"

// The above one would be here, too

int main(int argc, const char* argv[]) {
  int i;
  i = 0;
  cout << "Linear Equation Calculator" << endl << "Copyright (c) 2011 Patrick Devaney" << endl
  << "Licensed under the Apache License Version 2" << endl;
  // This loop makes the code a bit messy,
  // but it's worth it so the program doesn't
  // crash if one enters random crap such as
  // "zrgxvd" or "54336564358"
  while(i < 1) {
    cout << "Type:" << endl
    << "0 to calculate a slope (the M value) based on two points on a line" << endl
    << "1 to calculate the Y-intercept (the B value) based on two points and a slope" << endl
    << "2 to calculate the slope (the M value) based on the Y-intercept and X and Y" << endl <<
    "plug-ins" << endl
    << "3 to find the next point up or down a line based on the slope (M) and X and Y"
    << endl << "plug-ins" << endl
    << "4 to find a point x positions down the line based on the slope (M) and X and Y"
    << endl << "plug-ins" << endl
    << "5 to find the equation of a parallel line in form y=mx+c"
    << endl << "plug-ins" << endl;

    string selection;
    cin >> selection;
    if(selection == "0") {
      mcalcxyplugin();
      i++;
    }
    else if(selection == "1") {
      calcbxymplugin();
      i++;
    }
    else if(selection == "2") {
      calcmxybplugin();
      i++;
    }
    else if(selection == "3") {
      calcpointxymplugin(1);
      i++;
    }
    else if(selection == "4") {
      int a;
      cout << "How many points up/down the line do you want? (Positive number for points" << endl
      << "further up, negative for previous points" << endl;
      cin >> a;
      calcpointxymplugin(a);
      i++;
    }
    else if(selection == "5"){

      calcparallelplugin();
      i++;
    }
    else {
      i = 1;
    }
    // End of that loop below
  }
  return 0;
}

Answer 1

在此范围内未声明的错误意味着这一点。在所有#include<...>文件都包含在主文件中之后，编译器找不到该函数，因此它不知道该怎么做。

但是，这也适用于另一种情况：

#include <iostream>

int main(int argc, char** argv)
{
    testfunc();
}

void testfunc()
{
    std::cout << "test!" << std::endl;
}

在这种情况下，问题的原因是编译器需要向前声明函数 - 即它需要函数原型。这将有效：

#include <iostream>

void testfunc(); // the compiler sees this and knows the linker
                 // has the responsibility of finding this symbol.

int main(int argc, char** argv)
{
    testfunc();
}

void testfunc()
{
    std::cout << "test!" << std::endl;
}

关于范围界定还有另一个案例。命名空间会影响范围，例如：

#include <iostream>

void testfunc();

int main(int argc, char** argv)
{
    testfunc();
}

namespace test
{
    void testfunc()
    {
        std::cout << "test!" << std::endl;
    }
}

也会失败。对于您的原型，您需要void test::testfunc();。这是因为命名空间的内部本身就是一个范围，而不是全局范围::。通过在代码中编写using namespace std;，您可以在全局命名空间中的std中使用函数。

我还注意到您使用.cpp作为您的包含。约定是对头文件使用.h或.hpp，头文件通常包含相应.cpp实现的前向声明，类等。

所以，我会检查一下：

代码不是命名空间。
你包括正确的事。
您正在使用正确的名称调用该函数。

1最终编译器错误:(有人可以为我解释真正的简单

1 个答案: