help: sizeof(struct)

help: sizeof(struct)

[lium]

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Hi,
	
	there is a struct like following:
	
	struct test {
		unsigned char a;
		unsigned int b;
		unsigned char c;
	}
	my target machine is ARM7TDMI, my gcc version is: "gcc version 3.0". when i use sizeof(struct test), it return 0xc. if i add 'packed' attribute, sizeof return 6. but i need the sizeof macro return 9. 
	
    the follow is memory layout:                    
                                                    
Normal: +---+---+---+---+  Packed: +---+---+---+---+
        |///|///|///|///|          |///|///|///|///|
        +---+---+---+---+          +---+---+---+---+
        | a |   |   |   |          | a | b | b | b |
        +---+---+---+---+          +---+---+---+---+
        | b | b | b | b |          | b | c |///|///|
        +---+---+---+---+          +---+---+---+---+
        | c |   |   |   |          |///|///|///|///|
        +---+---+---+---+          +---+---+---+---+
                                                    
Wanted: +---+---+---+---+                           
        |///|///|///|///|                           
        +---+---+---+---+                           
        | a |   |   |   |                           
        +---+---+---+---+                           
        | b | b | b | b |                           
        +---+---+---+---+                           
        | c |///|///|///|                           
        +---+---+---+---+         

	would you please tell me which compiling option can do so.

	                 



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Re: help: sizeof(struct)

[Claudio Bley]

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>>>>> "lium" == lium  <lium@i-net.com.cn> writes:

    lium> Hi, there is a struct like following:
	
    lium> 	struct test { unsigned char a; unsigned int b;
    lium> unsigned char c; } my target machine is ARM7TDMI, my gcc
    lium> version is: "gcc version 3.0". when i use sizeof(struct
    lium> test), it return 0xc. if i add 'packed' attribute, sizeof
    lium> return 6. but i need the sizeof macro return 9.
	
You may use the following code:

struct test {
        unsigned char a ;
        int : 24; /* unused */
        unsigned int b;
        unsigned char c;
} __attribute__((__packed__));


HTH
Claudio
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