检查命令行输入是否为数字 [英] check that command line input is numeric

问题描述

我是C语言的新手，想编写一个简单的程序，用正好两个命令行参数来调用（第一个是程序的名称，第二个是字符串）。
我已经验证了参数的 number ，现在想验证输入中仅包含数字。

I'm new to C and want to write a simple programme to be called with exactly two command line arguments (the first one being the programme's name, the second one being a string). I have validated the number of arguments and now want to validate the input only contains digits.

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <cs50.h>

int main(int argc, string argv[])
{
    if (argc == 2)
        {
            for (int i = 0, n = strlen(argv[1]); i < n; i++)
            {
                if isdigit(argv[1][i])
                {
                    printf("Success!\n");
                }
                else
                    {
                    printf("Error. Second argument can be numbers only\n");
                    return 1;
                    }    
            }
    else
        {
            printf("Error. Second argument can be numbers only\n");
            return 1;
        }
}

虽然上面的代码没有引发错误，但是无法正确验证输入，我不知道为什么。有人可以指出我正确的方向吗？

While the above code doesn't throw errors, it doesn't correctly validate the input and I can't figure out why. Could someone point me in the right direction?

请多多关照，并尽一切努力

Thanks a lot in advance and all the best

推荐答案

if (argc != 2)

必须是

if (argc == 2)

---

做

---

Doing

if isdigit(argv[1][i])
{
  printf("Success!\n");
}

如果数字有4位数字，则您将打印4次成功，更好做类似的事情：

you will print "Success" 4 times if the number has 4 digits, better to do something like :

for (int i = 0, n = strlen(argv[1]); i < n; i++)
{
   if (!isdigit(argv[1][i])
   {
     printf("Error. Second argument can be numbers only\n");
     return 1;
   }    
 }
 printf("Success!\n");
 return 0;

---

示例：

---

Example :

#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main(int argc, char * argv[])
{
  if (argc == 2)
  {
    int i, n;

    for (i = 0, n = strlen(argv[1]); i < n; i++)
    {
      if (!isdigit(argv[1][i]))
      {
        printf("Error. Second argument can be numbers only\n");
        return 1;
      }
    }
    printf("Success!\n");
  }
  else {
    puts("argument is missing");
    return 1;
  }

  return 0;
}

编译和执行：

pi@raspberrypi:/tmp $ gcc -pedantic -Wextra c.c
pi@raspberrypi:/tmp $ ./a.out 
argument is missing
pi@raspberrypi:/tmp $ ./a.out az
Error. Second argument can be numbers only
pi@raspberrypi:/tmp $ ./a.out 12
Success!
pi@raspberrypi:/tmp $ ./a.out 12a
Error. Second argument can be numbers only
pi@raspberrypi:/tmp $ 

在valgrind下执行：

Execution under valgrind :

pi@raspberrypi:/tmp $ valgrind ./a.out 123
==2051== Memcheck, a memory error detector
==2051== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==2051== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==2051== Command: ./a.out 123
==2051== 
Success!
==2051== 
==2051== HEAP SUMMARY:
==2051==     in use at exit: 0 bytes in 0 blocks
==2051==   total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==2051== 
==2051== All heap blocks were freed -- no leaks are possible
==2051== 
==2051== For counts of detected and suppressed errors, rerun with: -v
==2051== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)

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