C ++ .NET - 如何处置一个位图？ [英] C++ .NET - how to dispose a bitmap?

问题描述

我想从文件中加载一个位图，就可以执行某些操作，并将其保存回相同的文件名。该模式是这样的：

 位图= gcnew位图（文件名）;
位图OUT = gcnew位图（in.Width，in.Height，in.PixelFormat）;填写[OUT]从数据[中]out.Save（文件名）;
 

但是，这并不正常工作。这是显而易见的。我不能保存到它仍然是打开的（因为位图中）的文件。现在的问题是：如何赫克我在收位图？我尝试过很多方法，但没有任何工程。调用Dispose曾在C＃中，但这种方法在C ++中保护。调用删除也不起作用。有什么解决办法？

编辑：
操作上一个位图也不起作用。但是，我发现了一个问题。调用delete工作。我忘了要申报位图指针

 位图^ =中的位图gcnew（文件名）;
位图^ OUT = gcnew位图（in.Width，in.Height，in.PixelFormat）;填写[OUT]从数据[中]删除;
out.Save（文件名）;
 

解决方案

这是在C ++ / CLI编码一种常见的陷阱，你使用栈语义。换句话说，你没有申报与 ^ 帽子引用类型变量。这使得在编译的范围块结束时自动发出的Dispose（）电话。非常方便，在C RAII 模式的模拟++，但在这里碍事。你要保存新位图前处置在位。

两种方法可以做到这一点。你可以通过添加括号玩范围盖帽：

 位图^出来;
尝试{
    {
        在（文件名）位图;
        OUT = gcnew位图（in.Width，in.Height，in.PixelFormat）;
        //等。
    } //＆LT; ==中的在这里得到处理
    输出＆GT;保存（文件名）;
}
最后{
    删除了;
}
 

但是，这是有点难看，特别是因为它需要在这个具体案例中混了退出。另一种方法是刚做的一切明确的：

 位图^出来;
位图^的;
尝试{
    在= gcnew位图（文件名）;
    OUT = gcnew位图（包含在＆GT;宽度，在 - ＆GT;的身高，在 - ＆GT;的PixelFormat）;
    //等。
    删除;
    在= nullptr;
    输出＆GT;保存（文件名）;
}
最后{
    删除;
    删除了;
}
 

I want to load a bitmap from file, perform some operations on it, and save it back under the same file name. The pattern is this:

Bitmap in = gcnew Bitmap(fileName);
Bitmap out = gcnew Bitmap(in.Width, in.Height, in.PixelFormat);

fill [out] with data from [in]

out.Save(fileName);

but this doesn't work. That's obvious. I cannot save to a file which is still opened (because of bitmap in). The question is: how the heck do I close bitmap in?! I've tried many ways but nothing works. Calling Dispose worked in C# but this method is protected in C++. Calling delete also doesn't work. What's the solution?

EDIT: Operating on one bitmap doesn't work either. But I found a problem. Calling delete worked. I forgot to declare my bitmaps as pointers

Bitmap^ in = gcnew Bitmap(fileName);
Bitmap^ out = gcnew Bitmap(in.Width, in.Height, in.PixelFormat);

fill [out] with data from [in]

delete in;
out.Save(fileName);

解决方案

This is a common trap in C++/CLI coding, you are using stack semantics. In other words, you didn't declare the reference type variable with the ^ hat. Which makes the compiler automatically emit the Dispose() call at the end of the scope block. Very convenient and a simulation of the RAII pattern in C++ but it gets in the way here. You want to dispose the in bitmap before saving the new bitmap.

Two ways to do this. You could play a game with the scope blocks by adding braces:

Bitmap^ out;
try {
    {
        Bitmap in(fileName);
        out = gcnew Bitmap(in.Width, in.Height, in.PixelFormat);
        // etc..
    }   // <== "in" gets disposed here
    out->Save(fileName);
}
finally {
    delete out;
}

But that's kinda ugly, especially since it needs to be mixed up for out in this very specific case. The alternative is to just do everything explicitly:

Bitmap^ out;
Bitmap^ in;
try {
    in = gcnew Bitmap(fileName);
    out = gcnew Bitmap(in->Width, in->Height, in->PixelFormat);
    // etc..
    delete in;
    in = nullptr;
    out->Save(fileName);
}
finally {
    delete in;
    delete out;
}

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