C語言運算式求值順序

一個C語言程式jiajia.c如下： 

#include<stdio.h>int main(){ long i; i=0; printf("%ld\n",(++i)+(++i)+(++i)); }

該程式在X86、linux機器上編譯後的運行結果為7，而在SPARC/SUNOS機器上編譯後的運行結果為6.試分析結果不同的原因。

jiajia.s

.file"jiajia.c".section.rodata.LC0:.string"%ld\n".text.globlmain.typemain, @functionmain:.LFB0:.cfi_startprocpushq%rbp.cfi_def_cfa_offset 16.cfi_offset 6, -16movq%rsp, %rbp.cfi_def_cfa_register 6subq$16, %rspmovq$0, -8(%rbp)addq$1, -8(%rbp)addq$1, -8(%rbp)//i先增加2，i=2movq-8(%rbp), %rax//移入i至DX寄存器leaq(%rax,%rax), %rdx//i+i=4addq$1, -8(%rbp)//i增加，i=3movq-8(%rbp), %rax//移入i至AX寄存器addq%rdx, %rax//4+3=7，結果存AX寄存器movq%rax, %rsimovl$.LC0, %edimovl$0, %eaxcallprintfleave.cfi_def_cfa 7, 8ret.cfi_endproc.LFE0:.sizemain, .-main.ident"GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3".section.note.GNU-stack,"",@progbits

jiajia2.c

#include<stdio.h>int main(){ long i; i=0; printf("%ld\n",(++i)+((++i)+(++i))); //改為後兩個加括弧}

結果輸出9

jiajia2.s

.file"jiajia2.c".section.rodata.LC0:.string"%ld\n".text.globlmain.typemain, @functionmain:.LFB0:.cfi_startprocpushq%rbp.cfi_def_cfa_offset 16.cfi_offset 6, -16movq%rsp, %rbp.cfi_def_cfa_register 6subq$16, %rspmovq$0, -8(%rbp)addq$1, -8(%rbp)addq$1, -8(%rbp)addq$1, -8(%rbp)//i增加至3，i=3movq-8(%rbp), %raxleaq(%rax,%rax), %rdx//i+i=6movq-8(%rbp), %raxaddq%rdx, %rax//3+3=9movq%rax, %rsimovl$.LC0, %edimovl$0, %eaxcallprintfleave.cfi_def_cfa 7, 8ret.cfi_endproc.LFE0:.sizemain, .-main.ident"GCC: (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3".section.note.GNU-stack,"",@progbits