Ada中的字符串处理 [英] String handling in Ada
问题描述
我正在尝试在Ada中定义一个字符串数组,以存储可变大小的字符串。
我的问题是我必须预先定义我在编译时不知道的Strings的大小,并且使用
Unbounded_Strings时String_Split.Create将无法工作,因为它需要Standard.String。
下面是我的代码,在这里我需要能够解析大小可变的字符串,而不仅仅是
固定长度的4。 / p>
预先感谢。
type StrArray是array(1 .. 7)的String(1..4);
函数Split(Line:String; Sep:String)return StrArray是
令牌:String_Split.Slice_Set;
输出:StrArray;
计数:自然:= 0;
开始
String_Split.Create(s =>令牌,
从=>行,
分隔符=> Sep,
模式=> String_Split.Single );
对于1中的I .. String_Split.Slice_Count(令牌)循环
Count:= Count + 1;
Output(Count):= String_Split.Slice(Tokens,I); -也不确定如何将Slice_Count转换为Integer!
结束循环;
返回输出;
结束分割;
GNAT的事实。 String_Split
使用 String
并不意味着您的 StrArray
必须使用。并且您需要迎合具有不同数量令牌的输入字符串,因此首先将 StrArray
声明为不受约束的数组类型:
类型StrArray是Ada.Strings.Unbounded.Unbounded_String;的数组(正范围<>)
;
现在 Split
开始如下:
函数Split(Line:String; Sep:String)return StrArray是
令牌:GNAT.String_Split.Slice_Set;
开始
(我们不能声明 Output
,我们不需要 Count
;我不得不去Google找出 String_Split
是GNAT实用程序包。)
要做的第一件事是拆分输入行,以便我们知道 Output
必须是(顺便说一句,您真的要 Single
吗?):
GNAT.String_Split.Create(S =>令牌,
从=>行,
分隔符=> Sep,
模式=> GNAT .String_Split.Single);
现在我们可以使用<声明 Output
code> Slice_Count 。注意转换为 Natural
(不是 Positive
;如果输入为空字符串,将没有标记,因此输出将是一个空数组,范围为 1 .. 0
)。
声明
输出:StrArray
(1 ..Natural(GNAT.String_Split.Slice_Count(Tokens)));
开始
现在填充输出
与令牌。 AdaCore选择将 Slice_Number
实现为 new Natural
,而不是实现为 Natural 的子类型。 code>,这就是为什么我们需要转换。
for Output'Range loop中的I
输出(I):=
Ada.Strings.Unbounded.To_Unbounded_String
(GNAT.String_Split.Slice
(令牌,GNAT.String_Split.Slice_Number(I)));
结束循环;
...并返回 Output
返回输出;
结尾;
结束分割;
要调用 Split
返回 StrArray
的长度,您事先不知道它的长度,可以使用受初始值限制:
declare
T:常量StrArray:=拆分(再见世界,);
在T'Range循环中以J开始
Ada.Text_IO.Put_Line('
& Ada.Strings.Unbounded.To_String(T(J))
&');
结束循环;
结尾;
I'm trying to define an array of Strings in Ada to store Strings of variable size. The problem I have is that I must pre-define the size of my Strings which I don't know at compile time, and with the Unbounded_Strings the String_Split.Create wouldn't work, as it requires Standard.String.
Below is my code, where I need to be able to parse Strings of variable size, and not just the fixed length 4.
Thanks in advance.
type StrArray is array(1..7) of String(1..4);
function Split(Line : String;Sep : String) return StrArray is
Tokens : String_Split.Slice_Set;
Output : StrArray;
Count : Natural := 0;
begin
String_Split.Create(s => Tokens,
From => Line,
Separators => Sep,
Mode => String_Split.Single);
For I in 1 .. String_Split.Slice_Count (Tokens) loop
Count := Count + 1;
Output(Count) := String_Split.Slice(Tokens,I); -- Not sure how to convert Slice_Count to Integer either!
end loop;
return Output;
end Split;
The fact that GNAT.String_Split
uses String
doesn’t mean that your StrArray
has to. And you need to cater for input strings with varying numbers of tokens, so begin by declaring StrArray
as an unconstrained array type:
type StrArray is array (Positive range <>)
of Ada.Strings.Unbounded.Unbounded_String;
Now Split
begins like this:
function Split (Line : String; Sep : String) return StrArray is
Tokens : GNAT.String_Split.Slice_Set;
begin
(we can’t declare Output
yet, and we won’t need Count
; and I had to go to Google to find out that String_Split
is a GNAT utility package).
The first thing to do is to split the input line, so that we know how large Output
needs to be (by the way, do you really want Single
?):
GNAT.String_Split.Create (S => Tokens,
From => Line,
Separators => Sep,
Mode => GNAT.String_Split.Single);
Now we can declare Output
using the Slice_Count
. Note the conversion to Natural
(not Positive
; if the input is an empty string, there will be no tokens, so the output will be an empty array, range 1 .. 0
).
declare
Output : StrArray
(1 .. Natural (GNAT.String_Split.Slice_Count (Tokens)));
begin
Now fill Output
with the tokens. AdaCore chose to implement Slice_Number
as new Natural
, rather than as a subtype of Natural
, which is why we need the conversion.
for I in Output'Range loop
Output (I) :=
Ada.Strings.Unbounded.To_Unbounded_String
(GNAT.String_Split.Slice
(Tokens, GNAT.String_Split.Slice_Number (I)));
end loop;
... and return Output
, within the declare block.
return Output;
end;
end Split;
To call Split
, which is going to return a StrArray
whose length you don’t know beforehand, you can use the technique of constraint by initial value:
declare
T : constant StrArray := Split ("goodbye world ", " ");
begin
for J in T'Range loop
Ada.Text_IO.Put_Line ("'"
& Ada.Strings.Unbounded.To_String (T (J))
& "'");
end loop;
end;
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