Originally posted by: SystemAdmin

> uname -a
AIX ep5512b 1 6 000497A2D900

> xlC -qversion
IBM XL C/C++ for AIX, V10.1
Version: 10.01.0000.0000
Hi

//

---

foo.cpp

---

#include <iostream>
struct Foo
{
unsigned char m1:1;
unsigned char m2:7;
};

int main()
{
std::cout << sizeof(Foo) << std::endl;
return 0;
}
//

---

> xlC foo.cpp
// No errors

> ./a.out
4 // not 1
// ==========
sizeof(Foo) on most of compilers is 1.
Do we have a way to say to compiler that sizeof(Foo) should be 1?

Thanks

Alex
#AIX-Forum

Originally posted by: shyhc

Probably not. I guess even

struct Foo 
{ unsigned 

char m1; 
};

would show up as 4 due to alignment reasons,
but anyway the compiler will treat the bitvector
as something longer no matter how many bits you allocate.
But there may be better forums for this...
#AIX-Forum

Originally posted by: TRB

I agree with shyhc, the reason has to do with allignment.

However, assuming you are using the AIX compiler, and further
assuming you NEED to sizeof to return 1, you can use the "-qalign=packed"
argument to the compiler which will change the alignment rules for
the whole program, or you can use a "pragma" to change the alignment
rules for a single structure.

Example of pragma:

#pragma options align=packed
struct Foo
{
unsigned char m1;
};
#pragma options align=reset

HTH,
-tony
#AIX-Forum

Originally posted by: SystemAdmin

Thanks

//

---

#include <iostream>

struct Foo0
{
unsigned char m1;
};

struct Foo1
{
unsigned char m1:1;
};
#pragma options align=bit_packed
struct Foo2
{
unsigned char m1:1;
};
#pragma options align=reset

int main()
{
std::cout << sizeof(Foo0) << std::endl;
std::cout << sizeof(Foo1) << std::endl;
std::cout << sizeof(Foo2) << std::endl;

return 0;
}
//

---

> ./a.out
1
4
1
#AIX-Forum