为什么＆QUOT; A +++++ B＆QUOT;不能在GCC编译，但＆QUOT; A +++ B＆QUOT;，＆QUOT; A ++ + ++ B＆QUOT;和＆QUOT; A +++ ++ B＆QUOT;可？

问题描述

Here is is the sample code, why "a+++++b" can not be compiled , but others can be?

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
    int a = 0;
    int b = 0;
    int c = 0;
    c = a+++b;
    printf("a+++b is: %d\n", c);

    c = a = b = 0;
    c = a++ + ++b;
    printf("a++ + ++b is: %d\n", c);

    c = b = a = 0;
    c = a+++ ++b;
    printf("a+++ ++b is: %d\n", c);

    c = b = a = 0;
    c = a+++++b;      // NOTE: Can not be compiled here.
    printf("a+++++b is: %d\n", c);

    return 0;
}

解决方案

That's because a+++++b is parsed as a ++ ++ + b and not as a ++ + ++ b[C's tokenizer is greedy]. a++ returns an rvalue and you cannot apply ++ on an rvalue so you get that error.

a+++b; // parsed as a ++ + b
a+++ ++b; // parsed as a ++ + ++ b

Read about Maximal Munch Rule.

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