How to find out the size of a structure without using sizeof
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Can we find out the size of a structure without using sizeof function? I have tried to write a macro passing the name of the structure as a parameter, but it did not work as expected!! Is there anyother way to do this? Please provide your valuable suggestions and code(if possible).....
R@j@$eg@r
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Can we find out the size of a structure without using sizeof function? I have tried to write a macro passing the name of the structure as a parameter, but it did not work as expected!! Is there anyother way to do this? Please provide your valuable suggestions and code(if possible).....
R@j@$eg@r
Yes.
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Can we find out the size of a structure without using sizeof function? I have tried to write a macro passing the name of the structure as a parameter, but it did not work as expected!! Is there anyother way to do this? Please provide your valuable suggestions and code(if possible).....
R@j@$eg@r
Homework-time, eh? Hint: You can get adresses of struct members...
Failure is not an option - it's built right in.
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Can we find out the size of a structure without using sizeof function? I have tried to write a macro passing the name of the structure as a parameter, but it did not work as expected!! Is there anyother way to do this? Please provide your valuable suggestions and code(if possible).....
R@j@$eg@r
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Even
sizeofusage is hazardous on Win32 structures. :)If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
Why?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Why?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Why?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Hint:
BITMAPINFO:-DIf the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
Is its size undetectable?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Since we are working on generating metadata about a structure by supplying the name of the structure, and getting its size during run time!!
R@j@$eg@r
This makes no sense. How does it answer the question, "Why is sizeof usage hazardous on Win32 structures?"
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Is its size undetectable?
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
Of course it is detectable. But its actual size cannot be detected with a naive use of
sizeof, i.e. it's tricky!:-DIf the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
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Of course it is detectable. But its actual size cannot be detected with a naive use of
sizeof, i.e. it's tricky!:-DIf the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
I agree. sizeof will return different size for the same structure if executed in different platforms i.e linux vs windows and thus different compilers. This is due to padding and alignment of members for optimization purposes in the memory. There are macros or compiler options that can be used to eliminate padding i.e to use 1 byte padding always. If i remember correctly this will be the "pack(1)" macro and in Visual C++ the compiler option /Z1 (I think) can be used to force 1 byte padding. This will give more consistent results with sizeof... :-).
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I agree. sizeof will return different size for the same structure if executed in different platforms i.e linux vs windows and thus different compilers. This is due to padding and alignment of members for optimization purposes in the memory. There are macros or compiler options that can be used to eliminate padding i.e to use 1 byte padding always. If i remember correctly this will be the "pack(1)" macro and in Visual C++ the compiler option /Z1 (I think) can be used to force 1 byte padding. This will give more consistent results with sizeof... :-).
Emmanouil wrote:
I agree. sizeof will return different size for the same structure if executed in different platforms i.e linux vs windows and thus different compilers.
I'm not exactly sure what you are agreeing to, but, for example,
sizeof(int)will also return different results on different platforms. That's not a fault with thesizeofoperator, however.
"A good athlete is the result of a good and worthy opponent." - David Crow
"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne
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Can we find out the size of a structure without using sizeof function? I have tried to write a macro passing the name of the structure as a parameter, but it did not work as expected!! Is there anyother way to do this? Please provide your valuable suggestions and code(if possible).....
R@j@$eg@r
There is some crap being posted here. The only time this is an issue is when you receive a pointer to a structure. If you receive a structure, the Compiler will know the size from the declaration. The Windows Standard way of dealing with pointers to structures of variable size is by using a member c_Bytes as the first member of a structure. This member must be guaranteed to always be initialised to the size of the structure. However, this is only the top of the iceberg, the problem is far larger, particularly if you deal with data structures generated by different compilers. For starters there is the Packing Method. The Structure {char Name[5],PhoneNumber[7]}; would by default be compiled into an object of 16 (NOT 12) bytes. An extra 3 bytes would be placed after Name to make PhoneNumber start at a DWORD boundary, and an extra byte would then be added to the entire structure, so that an array of it would have each element on a DWORD boundary. You can control this behaviour with a #pragma pack in the header file that declares the structure. (packing for a structure is set at Declaration level, NOT at Useage level). #pragma pack(1) would indeed create a 12 byte structure. Another issue is when you use structures generated by different compilers are dependent on issues of the kind of 'Howmany bytes does an int occupy'. You can circumvent a lot of this by using WORD and DWORD types, which most( but not All) compiler writers agree occupy 2 resp 4 bytes. Do not forget, an int under WIN16 was 2 Bytes, under WIN32 it is 4. So, the same Structure Declaration will lead to entrely different Sizes and Offsets under WIN16 compared to WIN32. Returning to your original question: Is there a (generic)way of determining the Size of a Structure without using the sizeof operator, the answer is No, Definitely Not. sizeof is not a function, it is a reserved name which the compiler at compile time resolves to the size of the object by reference to the symbol table. If the size is not known at compile time, the compiler provides NO alternative mechanism, you must create your own runtime mechanism to transmit the size of the object a pointer points to inside the object.
LateNightsInNewry
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There is some crap being posted here. The only time this is an issue is when you receive a pointer to a structure. If you receive a structure, the Compiler will know the size from the declaration. The Windows Standard way of dealing with pointers to structures of variable size is by using a member c_Bytes as the first member of a structure. This member must be guaranteed to always be initialised to the size of the structure. However, this is only the top of the iceberg, the problem is far larger, particularly if you deal with data structures generated by different compilers. For starters there is the Packing Method. The Structure {char Name[5],PhoneNumber[7]}; would by default be compiled into an object of 16 (NOT 12) bytes. An extra 3 bytes would be placed after Name to make PhoneNumber start at a DWORD boundary, and an extra byte would then be added to the entire structure, so that an array of it would have each element on a DWORD boundary. You can control this behaviour with a #pragma pack in the header file that declares the structure. (packing for a structure is set at Declaration level, NOT at Useage level). #pragma pack(1) would indeed create a 12 byte structure. Another issue is when you use structures generated by different compilers are dependent on issues of the kind of 'Howmany bytes does an int occupy'. You can circumvent a lot of this by using WORD and DWORD types, which most( but not All) compiler writers agree occupy 2 resp 4 bytes. Do not forget, an int under WIN16 was 2 Bytes, under WIN32 it is 4. So, the same Structure Declaration will lead to entrely different Sizes and Offsets under WIN16 compared to WIN32. Returning to your original question: Is there a (generic)way of determining the Size of a Structure without using the sizeof operator, the answer is No, Definitely Not. sizeof is not a function, it is a reserved name which the compiler at compile time resolves to the size of the object by reference to the symbol table. If the size is not known at compile time, the compiler provides NO alternative mechanism, you must create your own runtime mechanism to transmit the size of the object a pointer points to inside the object.
LateNightsInNewry
>>There is some crap being posted here. And you're validating the posted crap with your long winded diatribe ;P
Yours Truly, The One and Only!