C#try-catch-else

Question

从Python到C#的异常处理让我烦恼的一件事是,在C#中似乎没有任何指定else子句的方法.例如,在Python中我可以写这样的东西(注意,这只是一个例子.我不是问什么是读取文件的最佳方法):

try
{
    reader = new StreamReader(path);
}
catch (Exception)
{
    // Uh oh something went wrong with opening the file for reading
}
else
{
    string line = reader.ReadLine();
    char character = line[30];
}

从我在大多数C#代码中看到的,人们只会写下面的内容:

try
{
    reader = new StreamReader(path);
    string line = reader.ReadLine();
    char character = line[30];
}
catch (Exception)
{
    // Uh oh something went wrong, but where?
}

这样做的问题在于我不希望因为文件中的第一行不能包含超过30个字符而超出范围异常.我只想捕获与读取文件流有关的异常.我可以在C#中使用任何类似的构造来实现相同的功能吗？

Answer 1

捕获特定类别的异常

try
{
    reader = new StreamReader(path);
    string line = reader.ReadLine();
    char character = line[30];
}
catch (IOException ex)
{
    // Uh oh something went wrong with I/O
}
catch (Exception ex)
{
    // Uh oh something else went wrong
    throw; // unless you're very sure what you're doing here.
}

当然,第二个捕获是可选的.而且由于你不知道发生了什么,吞下这个最普遍的例外是非常危险的.

Answer 2

你可以这样写:

bool success = false;
try {
    reader = new StreamReader(path);
    success = true;
}
catch(Exception) {
    // Uh oh something went wrong with opening the file for reading
}
finally {
    if(success) {
        string line = reader.ReadLine();    
        char character = line[30];
    }
}   

Answer 3

你可以这样做:

try
{
    reader = new StreamReader(path);
}
catch (Exception)
{
    // Uh oh something went wrong with opening the file for reading
}

string line = reader.ReadLine();
char character = line[30];

但是,当然,您必须设置reader正确的状态或return方法.

Answer 4

捕获更具体的例外情况.

try {
   reader = new StreamReader(path);
   string line = reader.ReadLine();
   char character = line[30];
}
catch(FileNotFoundException e) {
   // thrown by StreamReader constructor
}
catch(DirectoryNotFoundException e) {
   // thrown by StreamReader constructor
}
catch(IOException e) {
   // some other fatal IO error occured
}

此外,通常,尽可能处理最具体的异常并避免处理基础System.Exception.