013 i 和 i的效率差别（013 efficiency difference between I and I）.docVIP

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013 i 和 i的效率差别（013 efficiency difference between I and I）.doc

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013 i 和 i的效率差别（013 efficiency difference between I and I）

013 i 和 i的效率差别（013 efficiency difference between I and I） 013 i++ and ++i efficiency difference between.Txt48 smile, is a green in spring, is under the sun hungry a shade, autumn is a cool breeze, a winter campfire. Smile to face it, you will feel the life is so warm. The efficiency difference between i++ and ++i A discussion of numerous issues, we finally see a person speaks fully and clearly. This post is shornmao (CAT) hair, I just helped him put it, that cat will not be angry with me. And First of all, a simple comparison of the efficiency of the prefix and suffix operator operator is one-sided, because there are many factors that influence the answer to this question. First consider the built-in data types: If the increment expression result is not used, but simply to increase one operand, the answer is clear, prefix and suffix method without any distinction, the compiler process should be the same, it is difficult to imagine what the compiler can make any difference in the create new styles between the two. Test C++ source code is as follows: //test1.cpp Void (test) { Int i=0; I++; ++i; } Gnu C/C++ 2 compiler assembler intermediate code is as follows: .file test1.cpp Gcc2_compiled: ___gnu_compiled_cplusplus: .text .align 4 .globl _test__Fv .def _test__Fv;.Scl 2;.Type 32;.Endef _test__Fv: Pushl%ebp Movl%esp,%ebp Subl $24,%esp Movl $0 -4 (%ebp); i=0 Incl -4 (%ebp); i++ Incl -4 (%ebp); ++i JMP L3 JMP L2 .p2align, 4, 7 L3: L2: Leave Ret Obviously, whether i++ or ++i is only a incl instruction. If the result of the expression is used, then the situation is slightly more complex. Test C++ source code is as follows: //test2.cpp Void (test) { Int i=0, a, b; A=i++; B=++i; } Gnu C/C++ 2 compiler assembler intermediate code is as follows: .file test2.cpp Gcc2_compiled: ___gnu_compiled_cplusplus: .text .align 4 .globl _test__Fv .def _test__Fv;.Scl 2;.Type 32;.Endef _test__Fv: Pushl%ebp Movl%esp,%ebp Subl $24,%esp Movl $0 -4 (%ebp); i=0 Movl -4 (%ebp),%eax; I / ax Movl%e