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~~