【问题标题】:Problem with c program to find the number of bits in a data typec程序查找数据类型中的位数的问题
【发布时间】:2019-09-26 01:57:54
【问题描述】:

我有一个任务是编写代码来查找某种数据类型可以容纳的最大值。我通过使用左移使用滚动 1 测试来执行此操作。它适用于 int、char、short int 和 long int,但是我无法让它为 unsigned in 和 unsigned char 工作。代码运行,但是当它到达那一点时,它就会卡住并且不输出任何东西。我将在下面附上我的整个代码。我怎样才能让它工作,我做错了什么。我确保使用 %u 而不是 %d,我不确定我还需要更改什么。谢谢!!

//
//  File name: ewh9320_proj2_data_types_rotate.c
//  Author: Ethan Hall
//  Created for RIT CMPR271 on 9/25/19
//  Purpose: To find the maximum value of bits used for each data type
//
#include <stdio.h>
#include <math.h>
int main(void)
{
    //int
    int overflow0, previous0;
    while(1)
    {
        previous0 = overflow0;
        overflow0 = 1 + (previous0<<1);
        if(previous0 > overflow0)
        {
            printf("int:\n");
            printf("The max value is %d\n\n", previous0);
            break;
        }
    }

    //char
    char overflow1, previous1;
    while(1)
    {
        previous1 = overflow1;
        overflow1 = 1 + (previous1<<1);
        if(previous1 > overflow1)
        {
            printf("char:\n");
            printf("The max value is %d\n\n", previous1);
            break;
        }
    }

    //short int
    short int overflow2, previous2;
    while(1)
    {
        previous2 = overflow2;
        overflow2 = 1 + (previous2<<1);
        if(previous2 > overflow2)
        {
            printf("short int:\n");
            printf("The max value is %d\n\n", previous2);
            break;
        }
    }

    //unsigned int
    unsigned int overflow3, previous3;
    while(1)
    {
        previous3 = overflow3;
        overflow3 = 1 + (previous3<<1);
        if(previous3 > overflow3)
        {
            printf("unsigned int:\n");
            printf("The max value is %u\n\n", previous3);
            break;
        }
    }

    //unsigned char
    unsigned char overflow4, previous4;
    while(1)
    {
        previous4 = overflow4;
        overflow4 = 1 + (previous4<<1);
        if(previous4 > overflow4)
        {
            printf("unsigned char:\n");
            printf("The max value is %d\n\n", previous4);
            break;
        }
    }

    //long int
    long int overflow5, previous5;
    while(1)
    {
        previous5 = overflow5;
        overflow5 = 1 + (previous5<<1);
        if(previous5 > overflow5)
        {
            printf("long int:\n");
            printf("The max value is %ld\n\n", previous5);
            break;
        }
    }

}


第二个不会超过 int64_t 的程序:


int main(void)
{
    //int8_t
    int8_t overflow0, previous0;
    while(1)
    {
        previous0 = overflow0;
        overflow0 = 1 + (previous0<<1);
        if(previous0 > overflow0)
        {
            printf("int8_t:\n");
            printf("The max value is %d\n\n", previous0);
            break;
        }
    }

    //uint8_t
    uint8_t overflow1, previous1;
    while(1)
    {
        previous1 = overflow1;
        overflow1 = 1 + (previous1<<1);
        if(previous1 > overflow1)
        {
            printf("uint8_t:\n");
            printf("The max value is %u\n\n", previous1);
            break;
        }
    }

    //int16_t
    int16_t overflow2, previous2;
    while(1)
    {
        previous2 = overflow2;
        overflow2 = 1 + (previous2<<1);
        if(previous2 > overflow2)
        {
            printf("int16_t:\n");
            printf("The max value is %d\n\n", previous2);
            break;
        }
    }

    //uint16_t
    uint16_t overflow3, previous3;
    while(1)
    {
        previous3 = overflow3;
        overflow3 = 1 + (previous3<<1);
        if(previous3 > overflow3)
        {
            printf("uint16_t:\n");
            printf("The max value is %u\n\n", previous3);
            break;
        }
    }

    //int32_t
    int32_t overflow4, previous4;
    while(1)
    {
        previous4 = overflow4;
        overflow4 = 1 + (previous4<<1);
        if(previous4 > overflow4)
        {
            printf("int32_t:\n");
            printf("The max value is %d\n\n", previous4);
            break;
        }
    }


    //uint32_t
    uint32_t overflow5, previous5;
    while(1)
    {
        previous5 = overflow5;
        overflow5 = 1 + (previous5<<1);
        if(previous5 > overflow5)
        {
            printf("uint32_t:\n");
            printf("The max value is %u\n\n", previous5);
            break;
        }
    }

    //int64_t
    int64_t overflow6, previous6;
    while(1)
    {
        previous6 = overflow6;
        overflow6 = 1 + (previous6<<1);
        if(previous6 >= overflow6)
        {
            printf("int64_t:\n");
            printf("The max value is %lld\n\n", previous6);
            break;
        }
    }

    //uint64_t
    uint64_t overflow7, previous7;
    while(1)
    {
        previous7 = overflow7;
        overflow7 = 1 + (previous7<<1);
        if(previous7 > overflow7)
        {
            printf("uint64_t:\n");
            printf("The max value is %llu\n\n", previous7);
            break;
        }
    }

    //uintptr_t
    uintptr_t overflow8, previous8;
    while(1)
    {
        previous8 = overflow8;
        overflow8 = 1 + (previous8<<1);
        if(previous8 > overflow8)
        {
            printf("uintptr_t:\n");
            printf("The max value is %lu\n\n", previous8);
            break;
        }
    }

    //intmax_t
    intmax_t overflow9, previous9;
    while(1)
    {
        previous9 = overflow9;
        overflow9 = 1 + (previous9<<1);
        if(previous9 > overflow9)
        {
            printf("intmax_t:\n");
            printf("The max value is %ld\n\n", previous9);
            break;
        }
    }
}

【问题讨论】:

  • unsigned char 循环中,在if 语句之前放置一个printf("%u %u\n", previous4, overflow4),看看会得到什么。
  • "int、...、short int 和 long int 都可以正常工作," --> 代码回复有符号整数溢出,这是 未定义的行为, `UB。

标签: c


【解决方案1】:

我实际上发现,通过在 if 语句中添加 >= 可以解决问题。谢谢!

【讨论】:

  • 但是我遇到了与相关程序有关的另一个问题。这使用滚动 1 个左移的相同方法来查找数据类型的最大值,但是使用不同的数据类型。通过无符号类型没有问题,但是一旦达到 int64_t,它就会卡住。我已将代码添加到第一篇文章中
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