C# 在不同编译下的不同表现

Posted 2022-05-30 tiancaiwrk

　　这是我在2018年的时候发在Unity Forums上的帖子, 至今无人回复, 之前是想用TypedReference做DataTable的相关功能的, 可是结果不正确.

tiancaiwrk, Oct 18, 2018 

System.TypedReference bugged? can‘t figure out how to use it !!!

C# has some way to get Generic Type target pointer, such as GCHandle / Marshal,
this time I want to use System.TypedReference for getting pointer of any struct, bug I think it‘s bugged...
I dont know how to report a BUG to Unity, just post it here
here is the code, it works in VS project but not unity project:

    void Start()
    
        int v1 = 100;
        int v2 = 1000;
 
        var m1 = __makeref(v1);
        var m2 = __makeref(v2);
 
        var val1 = __refvalue(m1, int);     // val1 is 100
        var val2 = __refvalue(m2, int);     // val2 is 1000
 
        Debug.Log(val1);
        Debug.Log(val2);
 
        unsafe
        
            *(IntPtr*)(&m1) = new IntPtr((void*)&v2); // 这里应该是把m1的值改变了的 m1应该为1000
 
            val1 = __refvalue(m1, int);     // val1 is 100 -- not changed 可是这里m1赋值没有变换, 还是100
            val2 = __refvalue(m2, int);     // val2 is 1000
 
            Debug.Log(val1);
            Debug.Log(val2);
 
            var ptr = *(IntPtr*)(&m1);
            var p = (int*)ptr.ToPointer();
            var data = *p;                  // data is 1000 -- changed 奇怪的是这里得到的m1的值又是1000
 
            Debug.Log(data);
        
    

And what‘s more, if I dont Set the pointer of m1, the value of [data] is Strange!!

    void Start()
    
        int v1 = 100;
        int v2 = 1000;
 
        var m1 = __makeref(v1);
        var m2 = __makeref(v2);
 
        var val1 = __refvalue(m1, int);     // val1 is 100
        var val2 = __refvalue(m2, int);     // val1 is 1000
 
        Debug.Log(val1);
        Debug.Log(val2);
 
        unsafe
        
            var ptr = *(IntPtr*)(&m1);
            var p = (int*)ptr.ToPointer();
            var data = *p;                  // data is 536019728 [random] -- WTF 更奇怪的是直接取m1的值, 居然不对
 
            Debug.Log(data);
        
    

This issue is happened in unity project, it works as expected in VS project.

the VS project value is :

 
        static unsafe void TT()
        
            int v1 = 100;
            int v2 = 1000;
 
            var m1 = __makeref(v1);
            var m2 = __makeref(v2);
 
            var val1 = __refvalue(m1, int);     // val1 is 100
            var val2 = __refvalue(m2, int);     // val2 is 1000
 
            unsafe
            
                *(IntPtr*)(&m1) = new IntPtr((void*)&v2);　　// m1值被赋值1000
 
                val1 = __refvalue(m1, int);     // val1 is 1000 VS工程编译的话, 这个m1值赋值正确的 1000
                val2 = __refvalue(m2, int);     // val2 is 1000
 
                var ptr = *(IntPtr*)(&m1);
                var p = (int*)ptr.ToPointer();
                var data = *p;                  // data is 1000 这里也是正确的
            
        

　　这个也是偶然想到极限速度对变量赋值的时候看到的做法, 测试以后发现不对劲. 以前大部分时候程序出错我们都会先想到是自己代码写错了, 不过这里可以看出

编译器也是有错的时候的......