* help: sizeof(struct)
@ 2002-07-15 19:49 lium
2002-07-16 2:19 ` Claudio Bley
0 siblings, 1 reply; 2+ messages in thread
From: lium @ 2002-07-15 19:49 UTC (permalink / raw)
To: gcc-help
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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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^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: help: sizeof(struct)
2002-07-15 19:49 help: sizeof(struct) lium
@ 2002-07-16 2:19 ` Claudio Bley
0 siblings, 0 replies; 2+ messages in thread
From: Claudio Bley @ 2002-07-16 2:19 UTC (permalink / raw)
To: gcc-help
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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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2002-07-15 19:49 help: sizeof(struct) lium
2002-07-16 2:19 ` Claudio Bley
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