Step to UEFI (15) —– 命令行参数 Again

前面介绍过 UEFI 下获得命令行参数的方法。这次尝试用 C Lib 来实现。

需要获取的参数直接用下面的代码进行输出

for (i=0;i<Argc; i++)
{
printf(“Arg[%d]: %s\n”,i,Argv[i]);
}

惊奇的发现,只能输出每个参数的第一个字母,一下子蒙了。琢磨了好长时间,忽然想起来这个应该是 unicode导致的。正常情况下

“abc”这样的ascii在unicode中会被存为 “97 00 98 0 99 0”,遇到 00 printf 自动就给截断了

顺手查了一下 \StdLib\Include\stdio.h ,其中提到了这个事情

If an l length modifier is present, the argument shall be a
pointer to the initial element of an array of wchar_t type. Wide
characters from the array are converted to multibyte characters
(each as if by a call to the wcrtomb function, with the conversion
state described by an mbstate_t object initialized to zero before
the first wide character is converted) up to and including a
terminating null wide character. The resulting multibyte characters
are written up to (but not including) the terminating null
character (byte). If no precision is specified, the array shall
contain a null wide character. If a precision is specified, no more
than that many bytes are written (including shift sequences, if
any), and the array shall contain a null wide character if, to
equal the multibyte character sequence length given by the
precision, the function would need to access a wide character one
past the end of the array. In no case is a partial multibyte
character written.

那我再试试

for (i=0;i<Argc; i++)
{
printf(“Arg[%d]: %ls\n”,i,Argv[i]);
}

结果依旧。不知道为什么了,如果有了解的朋友可以给我写邮件告诉我。

好在我们还有 Print 和 wprintf 可以绕过去。最后写了一个程序,主要代码如下

#include  <Uefi.h>
#include  <Library/UefiLib.h>
#include  <Library/ShellCEntryLib.h>

#include  <stdio.h>
#include <wchar.h>
/***
  Demonstrates basic workings of the main() function by displaying a
  welcoming message.

  Note that the UEFI command line is composed of 16-bit UCS2 wide characters.
  The easiest way to access the command line parameters is to cast Argv as:
      wchar_t **wArgv = (wchar_t **)Argv;

  @param[in]  Argc    Number of argument tokens pointed to by Argv.
  @param[in]  Argv    Array of Argc pointers to command line tokens.

  @retval  0         The application exited normally.
  @retval  Other     An error occurred.
***/
int
EFIAPI
main (
  IN int Argc,
  IN char **Argv
  )
{
  int i;
  printf("You have input %d args\n",Argc);

  printf("\nExp1. If we use \" printf(\"Arg[%%d]: %%s\\n\",i,Argv[i]);\n");
  for (i=0;i<Argc; i++)  
   {
	printf("Arg[%d]: %s\n",i,Argv[i]);
   }
  
  printf("\nExp2. If we use \" printf(\"Arg[%%d]: %%ls\\n\",i,Argv[i]);\n");
  for (i=0;i<Argc; i++)  
   {
	printf("Arg[%d]: %ls\n",i,Argv[i]);
   }
   
  printf("\nExp3. If we use \" Print(L\"Arg[%%d]: %%s\\n\",i,Argv[i]);\n");
  for (i=0;i<Argc; i++)  
   {
	Print(L"Arg[%d]: %s\n",i,Argv[i]);
   }

  printf("\nExp4. If we use \" wprintf(L\"Arg[%%d]: %%s\\n\",i,Argv[i]);\n");
  for (i=0;i<Argc; i++)  
   {
	wprintf(L"Arg[%d]: %ls\n",i,Argv[i]);
   }   
  return EFI_SUCCESS;
}

 

最终的运行结果

argv

代码下载:Main (和前面几篇文章一样,请用 AppPkg 编译)

Step to UEFI (15) —– 命令行参数 Again》上有 5 条评论

  1. snowman1101

    不知道为什么会有这样的结果 char的话就是单字节,不应该出现双字节的问题
    我在实机(x64)测试了一下 只有
    printf(“Arg[%d]: %s\n”,i,Argv[i]);
    会正常显示

    回复
  2. snowman1101

    按照你图片的结果,你应该是接收到了一个双字节字符串的指针。
    也许是EDK版本问题,也可能是SHELL的问题。
    总之你想要接收一个单字节的命令行地址,系统却传给你了一个双字节的。

    不过EDK中默认用的是双字节,而且上面也说了 想要访问命令行要转换类型
    Note that the UEFI command line is composed of 16-bit UCS2 wide characters.
    The easiest way to access the command line parameters is to cast Argv as:
    wchar_t **wArgv = (wchar_t **)Argv;

    可我在实机测试的结果却是接收到的单字节,也许是我用的shell 自动转换了?

    回复

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