使用C ++从.dll调用带有默认参数的函数 [英] Call function with default argument from .dll with c++

问题描述

我在.dll的标题中定义了一个函数

I have a function defined in the Header of my .dll

void calculo(vector<double> A, vector<int> B, double &Ans1, double jj);

在.cpp文件中的定义如下：

in the .cpp file it is defined as follows:

void calculo(vector<double> A, vector<int> B, double &Ans1, double jj = 36.5);

我正在使用以下代码从另一个C ++代码中调用此.dll：

I am calling this .dll from another c++ code using the following code:

#include "stdafx.h"
#include <windows.h>
#include <iostream>
#include <stdio.h>
#include "TEST_DLL.h"


typedef void(_stdcall *f_funci)(vector<double> A, vector<int> B, double &Ans1, double jj);

int main()
{

vector<double> A;
vector<int> B;
double ans1;
double teste;

HINSTANCE hGetProcIDDLL = LoadLibrary(L"MINHA_DLL.dll");
    if (!hGetProcIDDLL) {
        std::cout << "could not load the dynamic library" << std::endl;
        return EXIT_FAILURE;
    }


f_funci Resultado = (f_funci)GetProcAddress(hGetProcIDDLL, "calculo");
    if (!Resultado) {
        std::cout << "could not locate the function" << std::endl;
        return EXIT_FAILURE;
    }

Resultado(A,B, ans1, teste);

}

这样，如果我输入 jj 参数。但是，由于它在.dll中被定义为标准输入，因此在没有它的情况下也应该可以工作，但是如果我尝试不编译。在从.dll加载函数的过程中，有没有一种方法可以声明 jj 参数具有标准输入值？

This way the function works if I input the "jj" parameter. However as it is defined as an standard input in the .dll it should work also without it but if I try it do not compile. Is there a way that I could declare in the procedure of loading the function from the .dll that the "jj" parameter have a standard input value?

尝试使用 Resultado（A，B，ans1）; 生成以下错误：

trying to compile using Resultado(A,B, ans1); generates the following error:

error C2198: 'f_funci': too few arguments for call

推荐答案

默认参数：

仅在函数声明的参数列表中允许使用

Are only allowed in the parameter lists of function declarations

如果您不想默认标题中的参数，则可以通过重载该函数来完成您要执行的操作：

If you don't want to default the argument in the header you could accomplish what you're trying to do by overloading the function:

void calculo(const vector<double>& A, const vector<int>& B, double &Ans1, const double jj);
void calculo(const vector<double>& A, const vector<int>& B, double &Ans1) { calculo(A, B, Ans1, 36.5); }

作为奖励评论，请传递 vector s按常量引用，因为按值传递会导致潜在的昂贵复制成本。

As a bonus comment, please pass vectors by constant reference as passing by value incurs the potentially expensive copy cost.

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