【C语言】[EDK2]字符串基本操作

【C语言】字符串基本操作

注意：字符串以‘\0’结束
C语言中字符串的基本操作主要依赖于字符数组和指针。下面是一些常见的字符串操作：

1、字符串比较:

逐个比较两个字符串中的Unicode字符，直到发现第一个不匹配的字符为止。如果所有字符都匹配，则认为两个字符串相同。
返回0：如果FirstString和SecondString完全相同。
返回非零值：如果FirstString和SecondString的第一个不匹配字符之间存在差异，则返回这两个不匹配字符的Unicode码点之差。

Compares two Null-terminated Unicode strings, and returns the difference
  between the first mismatched Unicode characters.
 @param  FirstString   A pointer to a Null-terminated Unicode string.
  @param  SecondString  A pointer to a Null-terminated Unicode string.

  @retval 0      FirstString is identical to SecondString.
  @return others FirstString is not identical to SecondString.

**/
INTN
EFIAPI
StrCmp (
  IN      CONST CHAR16  *FirstString,
  IN      CONST CHAR16  *SecondString
  )
{
  //
  // ASSERT both strings are less long than PcdMaximumUnicodeStringLength
  //
  ASSERT (StrSize (FirstString) != 0);
  ASSERT (StrSize (SecondString) != 0);

  while ((*FirstString != L'\0') && (*FirstString == *SecondString)) {
    FirstString++;
    SecondString++;
  }

  return *FirstString - *SecondString;
}

2、字符串前几位比较

它用于比较两个以Null终止的Unicode字符串，但仅限于指定的字符数量（由参数Length决定）。这个函数的主要目的是在限定范围内判断两个字符串是否相同。

  @param  FirstString   A pointer to a Null-terminated Unicode string.
  @param  SecondString  A pointer to a Null-terminated Unicode string.
  @param  Length        The maximum number of Unicode characters to compare.

  @retval 0      FirstString is identical to SecondString.
  @return others FirstString is not identical to SecondString.

**/
INTN
EFIAPI
StrnCmp (
  IN      CONST CHAR16  *FirstString,
  IN      CONST CHAR16  *SecondString,
  IN      UINTN         Length
  )
{
  if (Length == 0) {
    return 0;
  }

  //
  // ASSERT both strings are less long than PcdMaximumUnicodeStringLength.
  // Length tests are performed inside StrLen().
  //
  ASSERT (StrSize (FirstString) != 0);
  ASSERT (StrSize (SecondString) != 0);

  if (PcdGet32 (PcdMaximumUnicodeStringLength) != 0) {
    ASSERT (Length <= PcdGet32 (PcdMaximumUnicodeStringLength));
  }

  while ((*FirstString != L'\0') &&
         (*SecondString != L'\0') &&
         (*FirstString == *SecondString) &&
         (Length > 1))
  {
    FirstString++;
    SecondString++;
    Length--;
  }

  return *FirstString - *SecondString;
}

3、在一个字符串里搜索另一个字符串是否存在

查找子串功能，该函数在给定的Unicode字符串String中查找指定的Unicode子字符串SearchString，并返回子字符串在原字符串中的起始地址，若未找到则返回NULL。

CHAR16 *
EFIAPI
StrStr (
  IN      CONST CHAR16  *String,
  IN      CONST CHAR16  *SearchString
  )
{
  CONST CHAR16  *FirstMatch;
  CONST CHAR16  *SearchStringTmp;

  //
  // ASSERT both strings are less long than PcdMaximumUnicodeStringLength.
  // Length tests are performed inside StrLen().
  //
  ASSERT (StrSize (String) != 0);
  ASSERT (StrSize (SearchString) != 0);

  if (*SearchString == L'\0') {
    return (CHAR16 *)String;
  }

  while (*String != L'\0') {
    SearchStringTmp = SearchString;
    FirstMatch      = String;

    while (  (*String == *SearchStringTmp)
          && (*String != L'\0'))
    {
      String++;
      SearchStringTmp++;
    }

    if (*SearchStringTmp == L'\0') {
      return (CHAR16 *)FirstMatch;
    }

    if (*String == L'\0') {
      return NULL;
    }

    String = FirstMatch + 1;
  }

  return NULL;
}

4、字符串大小写转换

将一个Unicode小写字母字符转换为其大写形式

CHAR16
EFIAPI
CharToUpper (
  IN      CHAR16  Char
  )
{
  if ((Char >= L'a') && (Char <= L'z')) {
    return (CHAR16)(Char - (L'a' - L'A'));
  }

  return Char;
}

5、获取字符串的长度

计算并返回一个以空字符(‘\0’)结束的ASCII字符串的长度。函数接受一个指向ASCII字符串的指针作为参数

  @param  String  A pointer to a Null-terminated ASCII string.

  @return The length of String.

**/
UINTN
EFIAPI
AsciiStrLen (
  IN      CONST CHAR8  *String
  )
{
  UINTN  Length;

  ASSERT (String != NULL);

  for (Length = 0; *String != '\0'; String++, Length++) {
    //
    // If PcdMaximumUnicodeStringLength is not zero,
    // length should not more than PcdMaximumUnicodeStringLength
    //
    if (PcdGet32 (PcdMaximumAsciiStringLength) != 0) {
      ASSERT (Length < PcdGet32 (PcdMaximumAsciiStringLength));
    }
  }

  return Length;
}

6、比较字符串的相同部分

函数用于比较两个ASCII字符串是否相等以及它们之间的相对顺序。返回值为0表示两个字符串完全相同，返回值不为0则表示两个字符串不相同，且返回值给出了第一个不同字符的ASCII值之差。

  @param  FirstString   A pointer to a Null-terminated ASCII string.
  @param  SecondString  A pointer to a Null-terminated ASCII string.

  @retval ==0      FirstString is identical to SecondString.
  @retval !=0      FirstString is not identical to SecondString.

**/
INTN
EFIAPI
AsciiStrCmp (
  IN      CONST CHAR8  *FirstString,
  IN      CONST CHAR8  *SecondString
  )
{
  //
  // ASSERT both strings are less long than PcdMaximumAsciiStringLength
  //
  ASSERT (AsciiStrSize (FirstString));
  ASSERT (AsciiStrSize (SecondString));

  while ((*FirstString != '\0') && (*FirstString == *SecondString)) {
    FirstString++;
    SecondString++;
  }

  return *FirstString - *SecondString;
}

7、复制源指针的内容到新的指针

用于复制指定长度的数据从源内存地址到目标内存地址

VOID
CopyMem (
  IN VOID   *Destination,
  IN VOID   *Source,
  IN UINTN  Length
  ) 
  {
  CHAR8 *Destination8;
  CHAR8 *Source8;

  Destination8  = Destination;
  Source8       = Source;
  while (Length--) {
    *(Destination8++) = *(Source8++);
  }
}

8、把指针长度里的值置0

将一段内存区域填充为0

VOID
ZeroMem (
  IN VOID   *Buffer,
  IN UINTN  Size
  )
  {
  INT8  *Ptr;

  Ptr = Buffer;
  while (Size--) {
    *(Ptr++) = 0;
  }
}

9、比较两个Guid是否一致

用于比较两个GUID（全局唯一标识符）是否相等。GUID是一个128位的数字，在许多操作系统和编程环境中用于唯一标识对象，如类、接口或其他资源。

函数接受两个参数：

  /*++

Routine Description:

  Compares to GUIDs

Arguments:

  Guid1 - guid to compare
  Guid2 - guid to compare

Returns:
  =  0  if Guid1 == Guid2
  != 0  if Guid1 != Guid2

--*/
INTN
CompareGuid (
  IN EFI_GUID     *Guid1,
  IN EFI_GUID     *Guid2
  ) {
  INT32 *g1;
  INT32 *g2;
  INT32 r;

  //
  // Compare 32 bits at a time
  //
  g1  = (INT32 *) Guid1;
  g2  = (INT32 *) Guid2;

  r   = g1[0] - g2[0];
  r |= g1[1] - g2[1];
  r |= g1[2] - g2[2];
  r |= g1[3] - g2[3];

  return r;
}

10、字符串的连接

将源字符串（包括终止空字符）追加到目标字符串的末尾

RETURN_STATUS
EFIAPI
StrCatS (
  IN OUT CHAR16        *Destination,
  IN     UINTN         DestMax,
  IN     CONST CHAR16  *Source
  );