结构体的内存存放是不是与编译器有关？

[吾非善类]

主程序如下
1 #include<stdio.h>
2 #include<stdlib.h>
3
4 #define _int64 long long
5
6 typedef struct Data_c{
7 char str[12];
8 _int64 a;
9 int b;
10 } Data;
11
12 int main(){
13 Data* dataP=(Data*)malloc(sizeof(Data));
14 printf("dataP address size is %lld\n",(dataP));
15 printf("dataP->a address size is %lld\n",&(dataP->a));
16 printf("subl dataP->a , dataP is %lld\n",(_int64)&(dataP->a)-(_int64)dataP);
17 *((_int64*)((_int64)dataP+16))=56;
18 printf("dataP->a is %lld\n",dataP->a);
19 return 0;
20 }
然后呢输出结果如下
$ ./a
dataP address size is 34359739296
dataP->a address size is 34359739312
subl dataP->a , dataP is 16
dataP->a is 56

按说，正确的应该是subl dataP->a,dataP 应该是12，为什么会变成了16呢？因为编译器原因吗？
我的编译器是windows下的cygwin64Terminal的gcc

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-cygwin/10/lto-wrapper.exe
Target: x86_64-pc-cygwin
Configured with: /mnt/share/cygpkgs/gcc/gcc.x86_64/src/gcc-10.2.0/configure --srcdir=/mnt/share/cygpkgs/gcc/gcc.x86_64/src/gcc-10.2.0 --prefix=/usr --exec-prefix=/usr --localstatedir=/var --sysconfdir=/etc --docdir=/usr/share/doc/gcc --htmldir=/usr/share/doc/gcc/html -C --build=x86_64-pc-cygwin --host=x86_64-pc-cygwin --target=x86_64-pc-cygwin --without-libiconv-prefix --without-libintl-prefix --libexecdir=/usr/lib --with-gcc-major-version-only --enable-shared --enable-shared-libgcc --enable-static --enable-version-specific-runtime-libs --enable-bootstrap --enable-__cxa_atexit --with-dwarf2 --with-tune=generic --enable-languages=c,c++,fortran,lto,objc,obj-c++ --enable-graphite --enable-threads=posix --enable-libatomic --enable-libgomp --enable-libquadmath --enable-libquadmath-support --disable-libssp --enable-libada --disable-symvers --with-gnu-ld --with-gnu-as --with-cloog-include=/usr/include/cloog-isl --without-libiconv-prefix --without-libintl-prefix --with-system-zlib --enable-linker-build-id --with-default-libstdcxx-abi=gcc4-compatible --enable-libstdcxx-filesystem-ts
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 10.2.0 (GCC)

[qzjhjxj]

结构体对齐的原因，参考：https://blog.csdn.net/qianghaohao/article/details/51011418?ops_request_misc=&request_id=&biz_id=102&utm_term=%E7%BB%93%E6%9E%84%E4%BD%93%E5%AF%B9%E9%BD%90%E5%8E%9F%E5%88%99&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduweb~default-8-51011418.pc_search_result_hbase_insert

[qzjhjxj]

https://blog.csdn.net/liran2019/article/details/106759881?ops_request_misc=&request_id=&biz_id=102&utm_term=%E7%BB%93%E6%9E%84%E4%BD%93%E5%AF%B9%E9%BD%90%E5%8E%9F%E5%88%99&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduweb~default-7-106759881.pc_search_result_hbase_insert

[真相重于对错]

内存对齐啊，64位应该是按8字节对齐的 vs的话可以用#pragma pack (4) ，修改它 gcc 这个语句是否管用，我没试过。 gcc好像可以用__attribute__ ((aligned (n)))，我没有gcc，没法试

[xian0-666]

结构体对齐并不是简单的相加，具体规范百度

[自信男孩]

打印地址，建议用%p，不建议用%lld，因为16进制看地址比较方便，第二个是%d是有符号数，而地址是无符号类型的数据。

[吾非善类]

谢谢各位大佬，明白了