动态链接库DLL的编写和调用(四则表达式计算)

在新建对话框上放置2个按钮（隐式和显式调用dll）和1个编辑框(连接变量m_exp)，添加按钮响应代码如下(隐式调用时：dll文件要放在对应目录[系统目录或者程序目录]下):

void CCalcTestDlg::OnButtonYinshi() 
{
    // TODO: Add your control notification handler code here
    UpdateData(true);
    if(m_exp.IsEmpty())
    {
        AfxMessageBox("请先输入四则运算表达式：");
        return;
    }
    if(!TestExp(m_exp))
    {
        AfxMessageBox("格式错，请输入类似 \n -(-5+3*2)/2+1 \n这样的四则表达式");
        return;
    }
    HMODULE hDll=::LoadLibrary(".\\Calc.dll");//加载链接库 
    if(hDll==NULL){ 
        MessageBox("找不到Calc.dll,加载动态链接库失败","Warning",MB_OK|MB_ICONWARNING); 
        return;} 
    typedef double (*pShow)(const char *); 
    pShow Show=(pShow)::GetProcAddress(hDll,"Calc"); 
    if(Show==NULL)
        MessageBox("函数调用失败","Warning",MB_OK|MB_ICONWARNING); //调用加载动态链接库失败
    else                 
        m_exp.Format("%f",Show(m_exp));     

    FreeLibrary(hDll);
    UpdateData(false);
}

void CCalcTestDlg::OnButtonXian() 
{
    // TODO: Add your control notification handler code here
    UpdateData(true);
    if(m_exp.IsEmpty())
    {
        AfxMessageBox("请先输入四则运算表达式：");
        return;
    }
    if(!TestExp(m_exp))
    {
        AfxMessageBox("格式错，请输入类似 \n -(-5+3*2)/2+1 \n这样的四则表达式");
        return;
    }
    CString filter,strPath;
    filter="Dll(*.dll)|*.dll||"; 
    CFileDialog dlg(TRUE,NULL,"Calc.dll",OFN_HIDEREADONLY,filter); 

    if(dlg.DoModal()==IDOK) 
        strPath=dlg.GetPathName(); 

    HMODULE hDll=::LoadLibrary(strPath);//加载链接库 
    if(hDll==NULL){ 
        MessageBox("加载动态链接库失败","Warning",MB_OK|MB_ICONWARNING); 
        return;} 
    typedef double (*pShow)(const char []); 
    pShow Show=(pShow)::GetProcAddress(hDll,"Calc"); 
    if(Show==NULL)
        MessageBox("函数调用失败","Warning",MB_OK|MB_ICONWARNING); //调用加载动态链接库失败
    else 
        m_exp.Format("%f",Show(m_exp)); 

    FreeLibrary(hDll);
    
    UpdateData(FALSE); 
}

bool CCalcTestDlg::TestExp(const char *str)
{
    char ch;
    int len=strlen(str),i=0;    
    while(len)
    {
        ch=*(str+i++);
        if(i==len+1)
                return true;
        if(ch>='0' &&ch<='9' || ch=='+' || ch=='-' || ch=='*' ||ch=='/' ||ch=='(' ||ch==')')
            ;
        else
            return false;
    }
    return true;        
}

这是用来做四则运算的，dll的编写如下(用MFC建立DLL工程):

//Calc.cpp
#include <math.h>
#define N 20
//函数格式如下
extern "C" __declspec(dllexport) double Calc(const char exp[])
{
    char ch;    
    //cout<<exp<<endl;
    int add(2),sub(3),mul(4),div(5),op[20],nc(0),oc(0);
    double num[N],rel(0);            
    for(int j=0;j<N;j++)
        num[j]=op[j]=0;
    j=0;
    int len=strlen(exp),i=-1;    
    while(++i<len)
    {
        ch=*(exp+i);    
        if(ch>='0' &&ch<='9' || ch=='+' || ch=='-' || ch=='*' ||ch=='/' ||ch=='(' ||ch==')')
            continue;        
        else                 
            return -99999999.99999;
    
    }
    //cout<<strlen(exp)<<endl;
    for(i=0;i<strlen(exp);i++)
    {    
        
        if(exp[i]<58 && exp[i]>47)    
        {            
            num[nc]=num[nc]*10+int(exp[i])-48;
            //cout<<num[nc]<<' ';
        }
        else 
        {
            //cout<<exp[i]<<' ';
            switch(exp[i])
        {
            case '+':
                op[oc++]=add;                
                break;
            case'-':
                op[oc++]=sub;                
                break;
            case'*':
                op[oc++]=mul;                
                break;
            case'/':
                op[oc++]=div;                
                break;
            case'(':
                add+=10;
                sub+=10;
                mul+=10;
                div+=10;
                break;
            case')':
                add-=10;
                sub-=10;
                mul-=10;
                div-=10;
                break;            
        }
        //cout<<op[oc-1]<<" ";
        }
        if(oc>nc)
        {
            if(op[oc]%10==2){
                op[oc--]=0;
                break;    }

            if(op[oc]%10==3)
                num[nc]=0;//"-x" => "0-x"
            nc++;
        }    
    }
    
    for(int w=0;w<20;w++)
    {
        j=0;
        if(op[0]==0)
            break;
        int temp=op[0]/2;            
        for(int i=0;i<20;i++)            
            if(op[i]/2>temp)
            {    
                j=i;
                temp=op[i]/2;
            }    
        switch(op[j]%10)
        {
        case 2:            
            rel=num[j]+num[j+1];        
            break;
        case 3:
            rel=num[j]-num[j+1];
            break;
        case 4:
            rel=num[j]*num[j+1];
            break;
        case 5:
            rel=num[j]/num[j+1];                    
            break;
        }
        temp=j;
        for(j;j<19;j++)
        {                
            op[j]=op[j+1];
            num[j]=num[j+1];
        }
        num[temp]=rel;        
    }
//    cout<<"The result is "<<num[0]<<endl;    
    return num[0];

}

这个程序运行后可以进行四则表达式运算(含括号、负号)，更多的格式暂时没时间做~~