Question

C#登陆失败，未处理FormatException，输入字符串的格式不正确。

错误代码 int state = Convert.ToInt32(cmd.ExecuteScalar());

登陆代码：
string strConnection = "Provider=Microsoft.Jet.OleDb.4.0;";

strConnection += @"Data Source=C:\Users\thtf\Desktop\新建文件夹\管理系统\管理系统\Database\xiangmu.mdb"; // 定义连接

OleDbConnection objConnection = new OleDbConnection(strConnection);

objConnection.Open();
string sql = "select * from login_user where username='" + this.txtusername.Text + "' and password='" + this.txtpassword.Text + "'";
OleDbCommand cmd = new OleDbCommand(sql, objConnection);
int state = Convert.ToInt32(cmd.ExecuteScalar());//执行sql语句，并返回获得值

if (state == 0)//如果数据中没有记录或有多条记录则抱错
{

MessageBox.Show("用户不存在，请检测用户名和密码是否正确！");

}
else
{
main2Form main2 = new main2Form();
main2.Show();
this.Hide();
}
objConnection.Close();

Answer 1

加个断点调试下，应该是有空格吧

Answer 2

C:\Users\thtf\Desktop\新建文件夹\管理系统\管理系统\Database\xiangmu.mdb不能是中文的

追问

改成英文的也不行

追答

select * from login_user where username='" + this.txtusername.Text + "' and password='" + this.txtpassword.Text + "'
改为
select count( *) from login_user where username='" + this.txtusername.Text + "' and password='" + this.txtpassword.Text + "'试试

Answer 3

//........
OleDbCommand cmd = new OleDbCommand(sql, objConnection);
object o = cmd.ExecuteScalar();
int state = (o == null || o is DBNull)?0:Convert.ToInt32(o);
//........