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C#: how to do: fixed (byte* ptr = (byte*)this) [on hold]

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0

I have a struct array in unmanaged memory.

In my struct code, marked as 'unsafe', I need to do something like:

void myMethod()

 fixed ( byte* ptr = this )
 
 MyStruct* pMyStruct = (MyStruct*)ptr;

 //-- from here on I can refer to the fields in the struct
 pMyStruct->Field1 = ...
 ...
 

Unfortunately, I am unable to cast/convert 'this' into a memory pointer.

My structs are all in unmanaged memory.

To get around the problem I defined all my struct methods as static and pass in the pointer to the start of the struct. Workable but not elegant.

Any ideas how to convert the 'this' to a 'byte*' or even a 'void*' ?

[For those who might want to question why I need this: for all its worth, the structs contain variable length fields. Each field is really a byte offset (from the start of the struct) to the actual value. The only things that have a a fixed offset into the structure are the offsets to the values. This means that where in memory the value of any field changes across struct instances - i.e., the location of the values are data dependent].

c# memory

share|improve this question

asked Mar 21 at 14:48

david marcusdavid marcus

726

put on hold as off-topic by Hans Passant, Sterling Archer, thehennyy, wp78de, thewaywewere Mar 21 at 17:23

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question was caused by a problem that can no longer be reproduced or a simple typographical error. While similar questions may be on-topic here, this one was resolved in a manner unlikely to help future readers. This can often be avoided by identifying and closely inspecting the shortest program necessary to reproduce the problem before posting." – Hans Passant, Sterling Archer, thehennyy, wp78de, thewaywewere

If this question can be reworded to fit the rules in the help center, please edit the question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What is the error message you are getting?
  
  – Robert Harvey♦
  Mar 21 at 14:53
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use Marshal object to copy any un-magnaged pointer object to managed object (or byte[]) array as long as you know the start location (the pointer) and the length of the object. Once you get it into managed memory you can use BitConverter to get the values.
  
  – jdweng
  Mar 21 at 14:56
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What is the type of this? Assuming myMethod() is a member of MyStruct, why are you trying to cast to byte* first and then back to MyStruct*?
  
  – kalimag
  Mar 21 at 14:56
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  The unsafe keyword is not a "now I can anything I want" passport. The C# compiler can already correctly detect that your assumptions are nonsensical.
  
  – Hans Passant
  Mar 21 at 15:13
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  this is not a pointer but a reference, even when referring to a struct. fixed ( MyStruct* ptr = &this) byte* b = (byte*) ptr; is legal. Whether your scenario makes sense is another matter altogether -- I strongly suspect it does not, so you should not take the indication that this compiles as confirmation that it will actually work correctly.
  
  – Jeroen Mostert
  Mar 21 at 16:18
  

  
  
  
  

 | 
show 5 more comments

0

I have a struct array in unmanaged memory.

In my struct code, marked as 'unsafe', I need to do something like:

void myMethod()

 fixed ( byte* ptr = this )
 
 MyStruct* pMyStruct = (MyStruct*)ptr;

 //-- from here on I can refer to the fields in the struct
 pMyStruct->Field1 = ...
 ...
 

Unfortunately, I am unable to cast/convert 'this' into a memory pointer.

My structs are all in unmanaged memory.

To get around the problem I defined all my struct methods as static and pass in the pointer to the start of the struct. Workable but not elegant.

Any ideas how to convert the 'this' to a 'byte*' or even a 'void*' ?

[For those who might want to question why I need this: for all its worth, the structs contain variable length fields. Each field is really a byte offset (from the start of the struct) to the actual value. The only things that have a a fixed offset into the structure are the offsets to the values. This means that where in memory the value of any field changes across struct instances - i.e., the location of the values are data dependent].

c# memory

share|improve this question

asked Mar 21 at 14:48

david marcusdavid marcus

726

put on hold as off-topic by Hans Passant, Sterling Archer, thehennyy, wp78de, thewaywewere Mar 21 at 17:23

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question was caused by a problem that can no longer be reproduced or a simple typographical error. While similar questions may be on-topic here, this one was resolved in a manner unlikely to help future readers. This can often be avoided by identifying and closely inspecting the shortest program necessary to reproduce the problem before posting." – Hans Passant, Sterling Archer, thehennyy, wp78de, thewaywewere

If this question can be reworded to fit the rules in the help center, please edit the question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What is the error message you are getting?
  
  – Robert Harvey♦
  Mar 21 at 14:53
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use Marshal object to copy any un-magnaged pointer object to managed object (or byte[]) array as long as you know the start location (the pointer) and the length of the object. Once you get it into managed memory you can use BitConverter to get the values.
  
  – jdweng
  Mar 21 at 14:56
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  What is the type of this? Assuming myMethod() is a member of MyStruct, why are you trying to cast to byte* first and then back to MyStruct*?
  
  – kalimag
  Mar 21 at 14:56
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  The unsafe keyword is not a "now I can anything I want" passport. The C# compiler can already correctly detect that your assumptions are nonsensical.
  
  – Hans Passant
  Mar 21 at 15:13
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  this is not a pointer but a reference, even when referring to a struct. fixed ( MyStruct* ptr = &this) byte* b = (byte*) ptr; is legal. Whether your scenario makes sense is another matter altogether -- I strongly suspect it does not, so you should not take the indication that this compiles as confirmation that it will actually work correctly.
  
  – Jeroen Mostert
  Mar 21 at 16:18
  

  
  
  
  

 | 
show 5 more comments

I have a struct array in unmanaged memory.

In my struct code, marked as 'unsafe', I need to do something like:

void myMethod()

 fixed ( byte* ptr = this )
 
 MyStruct* pMyStruct = (MyStruct*)ptr;

 //-- from here on I can refer to the fields in the struct
 pMyStruct->Field1 = ...
 ...
 

Unfortunately, I am unable to cast/convert 'this' into a memory pointer.

My structs are all in unmanaged memory.

To get around the problem I defined all my struct methods as static and pass in the pointer to the start of the struct. Workable but not elegant.

Any ideas how to convert the 'this' to a 'byte*' or even a 'void*' ?

[For those who might want to question why I need this: for all its worth, the structs contain variable length fields. Each field is really a byte offset (from the start of the struct) to the actual value. The only things that have a a fixed offset into the structure are the offsets to the values. This means that where in memory the value of any field changes across struct instances - i.e., the location of the values are data dependent].

c# memory

share|improve this question

asked Mar 21 at 14:48

david marcusdavid marcus

726

void myMethod()

 fixed ( byte* ptr = this )
 
 MyStruct* pMyStruct = (MyStruct*)ptr;

 //-- from here on I can refer to the fields in the struct
 pMyStruct->Field1 = ...
 ...
 

share|improve this question

asked Mar 21 at 14:48

david marcusdavid marcus

726

share|improve this question

asked Mar 21 at 14:48

david marcusdavid marcus

726

asked Mar 21 at 14:48

david marcusdavid marcus

726

asked Mar 21 at 14:48

david marcusdavid marcus

726