#pragma pack(push,1)

構造体などのアラインメント （16bit・32bit・64bit）をソースコードの途中で変更

pushとpop機能でネスト可能

#pragma pack(push,1)によって、アラインメントを1バイトに変更

cat pragma_pack_test.cpp
// pragma_pack_test.cpp
// console application

#using <mscorlib.dll>
#using <System.dll>

using namespace System;

#include "pragma_pack_test.h"
typedef struct s1_tag {
   
        char ch1; 
    int i1; 
	long l1;
} s1;
#pragma pack(push,1)
typedef struct s2_tag {
    char ch1; 
    int i1; 
	long l1;
} s2;
#pragma pack(pop)

int main(array<System::String ^> ^args){
	s1 t1;
	s2 t2;
    Console::WriteLine("size of t1={0}",sizeof(s1));
    Console::WriteLine("size of t2={0}",sizeof(s2));
	return EXIT_SUCCESS;
}




cat makefile
# makefile for pragma_pack_test
# console application

.PHONY: all test mmm clean 
.SUFFIXES: .exe .obj .txt .resources .dll

TARGET=pragma_pack_test

CULTUREDIRS=
DLLS=

all: $(TARGET).exe $(DLLS)


LOPT=

OBJS=$(TARGET).obj AssemblyInfo.obj

$(TARGET).obj: $(TARGET).cpp


AssemblyInfo.obj: AssemblyInfo.cpp

meta: $(TARGET).exe
	ILDasm /out:$@ /metadata $<

$(TARGET).exe: $(OBJS)  
	link $(LOPT) $^ 

.cpp.obj:
	#cl -c -Wall -Od -clr:safe $<
	cl -c -Wall -Od -clr $<

test: $(TARGET).exe
	./$(TARGET).exe 

clean:
	@-rm $(TARGET).exe *.obj *~ $(TARGET).exe.manifest 1>/dev/null 2>&1
	@-rm *.resources 1>/dev/null 2>&1
	@-rm -fr $(CULTUREDIRS)

mmm:
	cat $(TARGET).cpp
	cat AssemblyInfo.cpp
	@echo
	cat makefile

html:
	cat /dev/clipboard | code2html.exe | unix2dos

install: $(TARGET).exe
	cp $(TARGET).exe ~/bin
	cp $(TARGET).exe.manifest ~/bin

$ make -B test
#cl -c -Wall -Od -clr:safe pragma_pack_test.cpp
cl -c -Wall -Od -clr pragma_pack_test.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.42
for Microsoft (R) .NET Framework version 2.00.50727.312
Copyright (C) Microsoft Corporation.  All rights reserved.

pragma_pack_test.cpp
pragma_pack_test.cpp(12) : warning C4820: 's1_tag' : '3' bytes padding added aft
er data member 's1_tag::ch1'
    pragma_pack_test.cpp(23) : warning C4100: 'args' : unreferenced formal parameter

pragma_pack_test.cpp(25) : warning C4101: 't2' : unreferenced local variable
pragma_pack_test.cpp(24) : warning C4101: 't1' : unreferenced local variable
#cl -c -Wall -Od -clr:safe AssemblyInfo.cpp
cl -c -Wall -Od -clr AssemblyInfo.cpp
Microsoft (R) C/C++ Optimizing Compiler Version 14.00.50727.42
for Microsoft (R) .NET Framework version 2.00.50727.312
Copyright (C) Microsoft Corporation.  All rights reserved.

AssemblyInfo.cpp
link  pragma_pack_test.obj AssemblyInfo.obj
Microsoft (R) Incremental Linker Version 8.00.50727.42
Copyright (C) Microsoft Corporation.  All rights reserved.

./pragma_pack_test.exe

        size of t1=12
size of t2=9