Are C# structs and C structs the same? Help needed

[Angel]

I'm using several C functions (in a dll) that receive a struct as parameter.
Since I'm doing it in C#, I assume I need to recreate the struct in C# in
order to call the function with the required parameter. What would I need
to do in order to convert a struct that looks like this:

typedef struct
{

char rsvd0[4];
char iadl1[50+1];
char iadl2[50+1];
char ictyi[50+1];

struct { //nested struct
char a;
char b;
char c;
} foot;

ADSR_REC stack[10];
char rsvd4[194];
} DIR_PARM;

into a C# struct? I'm already able to call functions w/o parameters from my
application (through DllImport) but I'm having trouble calling a function
that requires this struct as parameter. And the "real" structure is
declared in Header file that I can't access (with #include). If I were doing
the program in C/C++ I would only need to include this header file and the
argument has to point to the struct. And how would I access DIR_PARM.foot.a
?

Any help would be appreciated.

 

[Willy Denoyette [MVP]]

Assuming char is Ansi 8 bit...

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct DIR_PARM
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=4)]
public char rsvd;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public char iadl1;
.....
public foot footer;
??? need to know the type of ADSR_REC
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
struct foot
{
char a;
char b;
char c;
}


Willy.

 

[Pete Davis]

In C++, struct and class are the same except that the default access level
of members in a class are private and in a struct they're public.

In C#, there are a lot more differences between a struct and a class. In C#:

1: structs are value types, classes are reference types
2: structs do not support inheritance
3: structs always have a default, no-parameter constructor, that can't be
replaced.
4: with structs, you can specify how fields are laid out in memory

(this list c/o Professional C#, 2nd edition)

In addition, I believe, though I'm not sure, that members of a struct
default to private access in C#.

Pete

 

[Angel]

Why do you declare the nested struct as public foot footer? And how would
I access the members of this structure?

ADSR_REC is another structure.

Thanks again.

Assuming char is Ansi 8 bit...

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct DIR_PARM
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=4)]
public char rsvd;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public char iadl1;
....
public foot footer;
??? need to know the type of ADSR_REC
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
struct foot
{
char a;
char b;
char c;
}


Willy.

I'm using several C functions (in a dll) that receive a struct as
parameter.
Since I'm doing it in C#, I assume I need to recreate the struct in C# in
order to call the function with the required parameter. What would I need
to do in order to convert a struct that looks like this:

typedef struct
{

char rsvd0[4];
char iadl1[50+1];
char iadl2[50+1];
char ictyi[50+1];

struct { //nested struct
char a;
char b;
char c;
} foot;

ADSR_REC stack[10];
char rsvd4[194];
} DIR_PARM;

into a C# struct? I'm already able to call functions w/o parameters from
my
application (through DllImport) but I'm having trouble calling a function
that requires this struct as parameter. And the "real" structure is
declared in Header file that I can't access (with #include). If I were
doing
the program in C/C++ I would only need to include this header file and the
argument has to point to the struct. And how would I access
DIR_PARM.foot.a
?

Any help would be appreciated.

 

[Willy Denoyette [MVP]]

Why do you declare the nested struct as public foot footer?

*** because it's a nested struct of type foot, or am I missing something?
And how would

I access the members of this structure?

*** DIR_PARM ar = new DIR_PARM();
ar.footer.a = 'x';

ADSR_REC is another structure.

Ok, but how does it looks like?

Willy.

 

[Stoitcho Goutsev \(100\) [C# MVP]]

Hi Angel,
Sinece foot is anonymous structure you can simply inline its members in
DIR_PARM.

If you use what Willy suggested you can access its mebers as

adsr_rect.footer.a = ....
adsr_rect i an instance of DIR_PARM structure.

You can find more info on
ms-help://MS.MSDNQTR.2003FEB.1033/cpguide/html/cpconstructssample.htm
or on-line:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconstructssample.asp


--
HTH
B\rgds
100

Why do you declare the nested struct as public foot footer? And how would
I access the members of this structure?

ADSR_REC is another structure.

Thanks again.

Assuming char is Ansi 8 bit...

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct DIR_PARM
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=4)]
public char rsvd;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public char iadl1;
....
public foot footer;
??? need to know the type of ADSR_REC
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
struct foot
{
char a;
char b;
char c;
}


Willy.

I'm using several C functions (in a dll) that receive a struct as
parameter.
Since I'm doing it in C#, I assume I need to recreate the struct in C# in
order to call the function with the required parameter. What would I need
to do in order to convert a struct that looks like this:

typedef struct
{

char rsvd0[4];
char iadl1[50+1];
char iadl2[50+1];
char ictyi[50+1];

struct { //nested struct
char a;
char b;
char c;
} foot;

ADSR_REC stack[10];
char rsvd4[194];
} DIR_PARM;

into a C# struct? I'm already able to call functions w/o parameters from
my
application (through DllImport) but I'm having trouble calling a function
that requires this struct as parameter. And the "real" structure is
declared in Header file that I can't access (with #include). If I were
doing
the program in C/C++ I would only need to include this header file and the
argument has to point to the struct. And how would I access
DIR_PARM.foot.a
?

Any help would be appreciated.

 

[Stoitcho Goutsev \(100\) [C# MVP]]

Hi Pete
In addition to what you said

4: with structs, you can specify how fields are laid out in memory

Even though the attribute is called StructLayoutAttribute it can be applied
to classes as well.
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
public sealed class StructLayoutAttribute : Attribute

In addition, I believe, though I'm not sure, that members of a struct

default to private access in C#.

Yes. All memebers of structs and classes default to *private*

--
B\rgds
100

Pete

--
http://www.petedavis.net

I'm using several C functions (in a dll) that receive a struct as parameter.
Since I'm doing it in C#, I assume I need to recreate the struct in C# in
order to call the function with the required parameter. What would I need
to do in order to convert a struct that looks like this:

typedef struct
{

char rsvd0[4];
char iadl1[50+1];
char iadl2[50+1];
char ictyi[50+1];

struct { //nested struct
char a;
char b;
char c;
} foot;

ADSR_REC stack[10];
char rsvd4[194];
} DIR_PARM;

into a C# struct? I'm already able to call functions w/o parameters from my
application (through DllImport) but I'm having trouble calling a function
that requires this struct as parameter. And the "real" structure is
declared in Header file that I can't access (with #include). If I were doing
the program in C/C++ I would only need to include this header file and the
argument has to point to the struct. And how would I access DIR_PARM.foot.a
?

Any help would be appreciated.

 

[Angel]

The documentation for the api says that the "argument must point to a
ZIP4_PARM structure".
My main concern is that since I don't know how the C function (in the dll)
accesses the struct (assuming it does it in C-style), how is it going to
know that the nested struct is not nested in the new struct? The CD with the
DLL comes from the US Postal Service, so I'm pretty sure it's compatible
with C#.
Also, one of the members of this struct is another struct (ADDR_REC) that's
composed three members of type char. How would I add this member of type
ADDR_REC to this struct?
In Parms.cs:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct ZIP4_PARM
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=4)]
string rsvd0;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public string iadl1;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public string iadl2;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public string ictyi;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=3)]
public string istai;

/**** This is the member I need to add. Would it use a MarshalAs? ****/
ADDR_REC stack[10];

public foot footer;

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
struct foot
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string a;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string b;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string c;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string d;
}

 

[Willy Denoyette [MVP]]

[MarshalAs(UnmanagedType.ByValArray, SizeConst=10)]
ADDR_REC[] stack;

...
}

struct ADDR_REC {
.....
}

Willy.

The documentation for the api says that the "argument must point to a
ZIP4_PARM structure".
My main concern is that since I don't know how the C function (in the dll)
accesses the struct (assuming it does it in C-style), how is it going to
know that the nested struct is not nested in the new struct? The CD with
the
DLL comes from the US Postal Service, so I'm pretty sure it's compatible
with C#.
Also, one of the members of this struct is another struct (ADDR_REC)
that's
composed three members of type char. How would I add this member of type
ADDR_REC to this struct?
In Parms.cs:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct ZIP4_PARM
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=4)]
string rsvd0;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public string iadl1;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public string iadl2;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=51)]
public string ictyi;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=3)]
public string istai;

/**** This is the member I need to add. Would it use a MarshalAs? ****/
ADDR_REC stack[10];

public foot footer;

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
struct foot
{
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string a;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string b;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string c;
[MarshalAs(UnmanagedType.ByValTStr, SizeConst=1)]
public string d;
}

I'm using several C functions (in a dll) that receive a struct as parameter.
Since I'm doing it in C#, I assume I need to recreate the struct in C# in
order to call the function with the required parameter. What would I
need
to do in order to convert a struct that looks like this:

typedef struct
{

char rsvd0[4];
char iadl1[50+1];
char iadl2[50+1];
char ictyi[50+1];

struct { //nested struct
char a;
char b;
char c;
} foot;

ADSR_REC stack[10];
char rsvd4[194];
} DIR_PARM;

into a C# struct? I'm already able to call functions w/o parameters from my
application (through DllImport) but I'm having trouble calling a function
that requires this struct as parameter. And the "real" structure is
declared in Header file that I can't access (with #include). If I were doing
the program in C/C++ I would only need to include this header file and
the
argument has to point to the struct. And how would I access DIR_PARM.foot.a
?

Any help would be appreciated.

 

[Stoitcho Goutsev \(100\) [C# MVP]]

Hi,

/**** This is the member I need to add. Would it use a MarshalAs? ****/
ADDR_REC stack[10];

Try to declare ADDR_REC's managed equivalent and then

in the ZIP4_PARM

....
[ MarshalAs( UnmanagedType.ByValArray, SizeConst=10)]
ADDR_REC[] stack;
.....

HTH
B\rgds
100

 

[Guest]

Hi Angel,

Is your problem resolved? Does the community's reply make sense to you?

If you still have anything unclear, please feel free to tell me, I will
help you.

Best regards,
Jeffrey Tan
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security
This posting is provided "as is" with no warranties and confers no rights.