阅读命令行参数

Question

can anyone point me to the problem over here? This compiles but it won't print anything. I need to compare the string from command line argument with the string "hello". Thanks!

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

  int main(int argc, char *argv[])
  { 
      if (argc == 0) 
      {
        printf("No arguments passed!\n");
      }

      char *str = argv[1];
      if(strcmp("hello", str)==0)
      {
        printf("Yes, I find it");     
      }

      else
      {
        printf("nothing"); 
      }

    return 0;
  }

Answer 1

My ESP suggests that you're running this in an interactive editor/debugger, such as Microsoft Studio. You probably haven't configured the environment to pass any command-line parameters, so you expect to see nothing as your output.

However, you access argv[1] , which does not exist, creating a seg-fault, and the program aborts before there is any output.

To fix this, check the value of argc first, and make sure you don't access invalid memory.

Also, I recommend putting a \\n at the end of each printf to help flush any buffered output to the console.

int main(int argc, char *argv[])
  {
      if (argc == 0) 
      {
        printf("No arguments passed!\n");
      }
      else if(strcmp("hello", argv[1])==0)
      {
        printf("Yes, I find it\n");     
      }

      else
      {
        printf("nothing\n"); 
      }

    return 0;
  }

When you run this, you should see:

$prompt:  myprogram
No arguments passed!

$prompt:  myprogram hello
Yes, I find it

$prompt:  myprogram world
nothing

Answer 2

The problem is the command you're using to run it. As you commented:

i run program > test hello or > test hi and the output is nothing

The > is redirecting output, and ends up giving you no command line arguments. What you want is simply program hello without the output redirection.

Answer 3

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

  int main(int argc, char *argv[])
  {
    if (argc < 2 || 0 != strcmp("hello", argv[1]))
        printf("nothing\n");     
      else
        printf("yes, found it\n"); 

    return 0;
  }

and output

bash-3.2$ gcc 1.c -o 1
    bash-3.2$ ./1 hello1
    nothing
    bash-3.2$ ./1 hello
    yes, found it
    bash-3.2$ ./1
    nothing

Answer 4

尝试将您的程序称为“测试”不同的东西