使用布尔值检查整数溢出

Question

这个小项目基于this discussion，关于在执行操作之前检测整数溢出的最佳方法。我想要做的是有一个程序演示使用整数检查的有效性。它应该对某些数字产生未经检查的整数溢出，而如果使用检查（-c）标志，它应该在执行操作之前退出。 -m 用于乘法。

程序在没有布尔部分的情况下运行良好，但我需要一些关于执行最高OneBitPosition 检查的布尔部分的帮助。添加真/假逻辑后出现编译错误。我不确定我是否正确调用和使用了highestOneBitPosition 函数。谢谢！

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*boolean */ 
#define true 1
#define false 0
typedef int bool;

void ShowUsage ()
{
    printf (
    "Integer Overflow Check before performing an arithmetic.\n"
    "=======================================================\n"
    "Usage:\n"
    "Integer Operant (-a, -s, -m, -d) Checked/Unchecked (-u, -c)\n"
    "Example: ./overflowcheck 2 -a 2 -u\n"
    "\n"
);
}

size_t highestOneBitPosition(uint32_t a) {
size_t bits=0;
while (a!=0) {
    ++bits;
    a>>=1;
};
return bits;
}

int main(int argc, char *argv[]) {
    if      (argc != 5) {ShowUsage (); return (0);}
    else if (strcmp(argv[2],"-m") == 0 && strcmp(argv[4],"-u") == 0)
            {printf("%s * %s = %d -- Not checked for integer overflow.\n",argv[1],argv[3], atoi(argv[1])*atoi(argv[3]));return 0;}
/*Works fine so far */
    else if (strcmp(argv[2],"-m") == 0 && strcmp(argv[4],"-c") == 0)
    {
    bool multiplication_is_safe(uint32_t a, uint32_t b) {
    a = atoi( argv[1] );
    b = atoi( argv[3] );
    size_t a_bits=highestOneBitPosition(a), b_bits=highestOneBitPosition(b);
    return (a_bits+b_bits<=32);}
        if (multiplication_is_safe==true) 
        {printf("%s * %s = %d -- Checked for integer overflow.\n",argv[1],argv[3], atoi(argv[1])*atoi(argv[3]));return 0;}
        if (multiplication_is_safe==false)
        {printf("Operation not safe, integer overflow likely.\n");}    
    }

    ShowUsage ();
    return (0);}

编译：

gcc integer_overflow2.c -o integer_overflow
integer_overflow2.c:40:61: error: function definition is not allowed here
        bool multiplication_is_safe(uint32_t a, uint32_t b) {
                                                            ^
integer_overflow2.c:45:17: error: use of undeclared identifier
      'multiplication_is_safe'
            if (multiplication_is_safe==true) 
                ^
integer_overflow2.c:47:17: error: use of undeclared identifier
      'multiplication_is_safe'
            if (multiplication_is_safe==false)
                ^

Answer 1

[渴望评论]

C 不支持嵌套函数。

正确缩进的 C 源代码可能如下所示：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*boolean */
#define true 1
#define false 0
typedef int bool;

void ShowUsage()
{
  printf("Integer Overflow Check before performing an arithmetic.\n"
      "=======================================================\n"
      "Usage:\n"
      "Integer Operant (-a, -s, -m, -d) Checked/Unchecked (-u, -c)\n"
      "Example: ./overflowcheck 2 -a 2 -u\n"
      "\n");
}

size_t highestOneBitPosition(uint32_t a)
{
  size_t bits = 0;
  while (a != 0)
  {
    ++bits;
    a >>= 1;
  };
  return bits;
}

bool multiplication_is_safe(uint32_t a, uint32_t b)
{
  a = atoi(argv[1]);
  b = atoi(argv[3]);
  size_t a_bits = highestOneBitPosition(a), b_bits = highestOneBitPosition(b);
  return (a_bits + b_bits <= 32);
}

int main(int argc, char *argv[])
{
  if (argc != 5)
  {
    ShowUsage();
    return (0);
  }
  else if (strcmp(argv[2], "-m") == 0 && strcmp(argv[4], "-u") == 0)
  {
    printf("%s * %s = %d -- Not checked for integer overflow.\n", argv[1],
        argv[3], atoi(argv[1]) * atoi(argv[3]));
    return 0;
  }

  /*Works fine so far */
  else if (strcmp(argv[2], "-m") == 0 && strcmp(argv[4], "-c") == 0)
  {
    if (multiplication_is_safe == true)
    {
      printf("%s * %s = %d -- Checked for integer overflow.\n", argv[1],
          argv[3], atoi(argv[1]) * atoi(argv[3]));
      return 0;
    }

    if (multiplication_is_safe == false)
    {
      printf("Operation not safe, integer overflow likely.\n");
    }
  }

  ShowUsage();
  return (0);
}

但是仍然存在一个错误，您可能希望自己找到并修复它。仔细查看编译器警告您的内容。要启用所有警告，请对 gcc 使用 -Wall -Wextra -pedantic。

Answer 2

查看以下链接： Nested function in C

标准 C 不支持嵌套函数。因此您会看到编译错误。 请将您的函数移到main() 之外，然后从main() 调用该函数