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C言語でa == 1 && a == 2 && a == 3をtrueにしてみたい

Last updated at Posted at 2018-01-21

C言語でもa == 1 && a == 2 && a == 3をtrueにしてみたい』の別アプローチ。
Core i7-5500U 2.40GHz + 16GB + Windows 10 + Cygwin64 の環境で gcc 6.4.0 を使用していますが環境に拠っては全然動かないかも。

hoge.c
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>

volatile int a = 1;

void* thread_func(void* vptr_args)
{
    (void)vptr_args;
    for (;;) {
        a = (a >= 3) ? 1 : a + 1;
    }
    return NULL;
}

int main(void)
{
    pthread_t thread;

    pthread_create(&thread, NULL, thread_func, NULL);
    for (;;) {
        if (a == 1 && a == 2 && a == 3) {
            printf("true\n");
            break;
        } else {
            printf("false\n");
        }
    }
    pthread_cancel(thread);
}
実行結果
$ gcc -O2 -Wall -Wextra hoge.c ; ./a|cat -n
     1  false
     2  false
     3  false
     4  false
     5  false
     6  false
     7  false
     8  false
     9  false
    10  false
    11  true

$

↑はたまたますごく早く終了した例。
wandboxで実行

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