Programming Forums > Application Development > C++

DBZ · Mar 17th, 2006, 10:22 PM

on this line
#define DO_INIT_STRUCT(ddstruct)
{
memset (&ddstruct, 0 , sizeof(ddstruct));
ddstruct.dwSize = sizeof(ddstruct);
}

What is missing up there? Cuz I kept getting an error
error C2447: missing function header (old-style formal list?)

Thxs

grumpy · Mar 17th, 2006, 10:57 PM

You really need to read the "How to post a question" sticky thread at the top of the C++ forum. That gives useful advice on how to ask questions to increase your chances of getting a useful answer.

That said, you got lucky..... this time. The answer to your question is that macros only work on one line by default. If you want a macro to work across multiple lines, you need to use a "continuation marker" so the preprocessor knows that what you intend. The "continuation marker" is a backslash on the end of ALL except the last line of the macro.

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#define DO_INIT_STRUCT(ddstruct)      \
{      \
memset (&ddstruct, 0 , sizeof(ddstruct));   \
ddstruct.dwSize = sizeof(ddstruct);    \
}

Note that there is no continuation marker on the last line.

If you want to be safer, you will actually do something like this;

(Toggle Plain Text)

#define DO_INIT_STRUCT(ddstruct)      \
do {      \
memset (&ddstruct, 0 , sizeof(ddstruct));   \
ddstruct.dwSize = sizeof(ddstruct);    \
} while(0)

One reason for the do {}while (0) surround is that, without them, the code;

(Toggle Plain Text)

if (some_condition)
   DO_INIT_STRUCT(some_struct);
else
   do_something_else();

will always generate a compiler error. With the do {} while (0) surround it will work as is usually intended.

DBZ · Mar 17th, 2006, 11:39 PM

sorry grumpy i didnt know how this forum systemw works and i did not intentionally do it on purpose. forgive me. but thxs for helping me out. Your a nice guy. Anyways, I will go and take a look through the rules of how to post....

Mar 17th, 2006, 10:22 PM	#1
DBZ Newbie Join Date: Feb 2006 Posts: 22 Rep Power: 0	Help with this. Can you check what's missing? on this line #define DO_INIT_STRUCT(ddstruct) { memset (&ddstruct, 0 , sizeof(ddstruct)); ddstruct.dwSize = sizeof(ddstruct); } What is missing up there? Cuz I kept getting an error error C2447: missing function header (old-style formal list?) Thxs

Mar 17th, 2006, 10:57 PM	#2
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,224 Rep Power: 5	You really need to read the "How to post a question" sticky thread at the top of the C++ forum. That gives useful advice on how to ask questions to increase your chances of getting a useful answer. That said, you got lucky..... this time. The answer to your question is that macros only work on one line by default. If you want a macro to work across multiple lines, you need to use a "continuation marker" so the preprocessor knows that what you intend. The "continuation marker" is a backslash on the end of ALL except the last line of the macro. (Toggle Plain Text) #define DO_INIT_STRUCT(ddstruct) \ { \ memset (&ddstruct, 0 , sizeof(ddstruct)); \ ddstruct.dwSize = sizeof(ddstruct); \ } #define DO_INIT_STRUCT(ddstruct) \ { \ memset (&ddstruct, 0 , sizeof(ddstruct)); \ ddstruct.dwSize = sizeof(ddstruct); \ } Note that there is no continuation marker on the last line. If you want to be safer, you will actually do something like this; (Toggle Plain Text) #define DO_INIT_STRUCT(ddstruct) \ do { \ memset (&ddstruct, 0 , sizeof(ddstruct)); \ ddstruct.dwSize = sizeof(ddstruct); \ } while(0) #define DO_INIT_STRUCT(ddstruct) \ do { \ memset (&ddstruct, 0 , sizeof(ddstruct)); \ ddstruct.dwSize = sizeof(ddstruct); \ } while(0) One reason for the do {}while (0) surround is that, without them, the code; (Toggle Plain Text) if (some_condition) DO_INIT_STRUCT(some_struct); else do_something_else(); if (some_condition) DO_INIT_STRUCT(some_struct); else do_something_else(); will always generate a compiler error. With the do {} while (0) surround it will work as is usually intended.

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Mar 17th, 2006, 11:39 PM	#3
DBZ Newbie Join Date: Feb 2006 Posts: 22 Rep Power: 0	sorry grumpy i didnt know how this forum systemw works and i did not intentionally do it on purpose. forgive me. but thxs for helping me out. Your a nice guy. Anyways, I will go and take a look through the rules of how to post....

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Programming Forums > Application Development > C++

Help with this. Can you check what's missing?