字符串?dāng)?shù)據(jù)類型是一個(gè)有序的字符集合。

字符串變量的長(zhǎng)度是集合中的字符數(shù)。

字符串類型的變量是動(dòng)態(tài)的，因?yàn)樗鼈兊拈L(zhǎng)度在仿真過(guò)程中可能會(huì)變化。

字符串中的單個(gè)字符變量的類型為byte。

Syntax:

string variable_name [= initial_value];

如果在聲明中未指定初始值，則將變量初始化為" "，一個(gè)空字符串?？兆址拈L(zhǎng)度為零。下面是一個(gè)字符串?dāng)?shù)據(jù)類型的示例：

module datatype1;
 string s1 = "hello";
 string s2 = "hello world";
 string s3 = "helloworld"; //  is ignored
 string s4, s5, s6;
 initial
 begin
 s4 = "later";
 s5 = ""; //empty string
 s6 = {"hi", s5}; //concatenation
 #10;
 $display ("s1=%s s2=%s s3=%s s4=%s s5=%s s6=%s", s1, s2, 
s3, s4, s5, s6);
 #100 $fnish;
 end 
 endmodule

在本例中，我們聲明了6個(gè)字符串，從s1到s6。s1、s2和s3分別進(jìn)行了初始化。其中字符串s3中的轉(zhuǎn)義字符()被轉(zhuǎn)義為空字符。

然后在“initial”語(yǔ)句塊中，將s4賦值為字符串“l(fā)ater”，將s5賦值為空字符串，并連接s5與" hi "，賦值給字符串s6。下面是仿真log:

ncsim> run
s1=hello s2=hello world s3=helloworld s4=later s5= s6=hi

String Operators

字符串?dāng)?shù)據(jù)類型還提供了處理字符串的操作符,如下表所示:

module datatype1; 
 string s2 = "hello world"; 
 string s3 = "helloworld"; 
 string s4, s5;
 string s6 = "compare"; 
 string s7 = "compare"; 
 string s8;
 integer s2len, s3len, s2c;
 initial begin
 #10; $display ("s2=%s s3=%s",s2,s3);
 #100 $fnish;
 end
 initial begin
 #15;
 s2len = s2.len( ); $display("String Length s2 = 
%0d",s2len); 
 s3len = s3.len( ); $display("String Length s3 = 
%0d",s3len);
 if (s2 == s3) $display("s2 = s3"); else $display("s2 
!= s3");
 if (s6 == s7) $display("s6 = s7"); else $display("s6 
!= s7");
 s4 = s2.substr(1,6);
 $display("s4 = %s",s4);
 s5 = "later ";
 s8 = {3{s5}};
 $display("s8 = %s",s8);
 S2c = s2[0];
 $display("s2c = %s",s2c);
 end 
 endmodule

在上面的例子中，聲明了字符串s2到s8并初始化為各種字符串。

將字符串長(zhǎng)度(.len())賦值給整數(shù)類型s2len和s3len。

比較字符串s2和s3以及字符串s6和
s7。

提取s2的部分字符串并將其賦值給s4。

復(fù)制s5三次，賦值給s8。

下面是仿真的log：

s2=hello world s3=helloworld
String Length s2 = 11
String Length s3 = 10
s2 != s3
s6 = s7
s4 = ello w
s8 = later later later
s2c = h
$fnish at simulation time 110
 V C S S i m u l a t i o n R e p o r t

String Methods

還有幾種方法可用于處理字符串，如下表所示：

module sMethods;
 string s1 = "hello";
 string s2 = "hello world";
 string s4;
 string s5 = "GOODBYE";

 byte x;
 integer s2len, s3len, i1, i2;
 initial
 begin
 #15;
 s2len = s2.len( );
 $display("String Length s2 = %0d",s2len);
 s1.putc(0,"C"); //replace 0'th character with 'C'
 $display("String s1 = %s",s1);
 x = s1.getc(0); //get 0'th character of string s1.
 $display("0'th character of string 'Cello' = %s",x);
 s4 = s2.toupper( ); //convert string 's2' to upper case
 $display("Upper Case of 'hello world' = %s",s4);
 s4 = s5.tolower ( );
 $display("Lower case of 'GOODBYE' = %s",s4);

 end
 endmodule

以及仿真log:

String Length s2 = 11
String s1 = Cello
0'th character of string 'Cello' = C
Upper Case of 'hello world' = HELLO WORLD
Lower case of 'GOODBYE' = goodbye
 V C S S i m u l a t i o n R e p o r t

在上面的例子中，

聲明一些字符串變量。在“initial”語(yǔ)句塊中，我們首先得到字符串(s2 = " hello world ";)的長(zhǎng)度11。

然后使用" putc "方法給字符串" s1 "的第0個(gè)字符加上字符" C ":

s1.putc(0,“C”);

由于s1字符串是“hello”，它現(xiàn)在變成“Cello”。然后，得到字符串s1的第0個(gè)字符(現(xiàn)在是“Cello”):

x = s1.getc (0);

我們使用.toupper方法將" s2 "字符串(s2 = " hello world ")轉(zhuǎn)換為全大寫，并將結(jié)果存儲(chǔ)在字符串" s4 "中:

s4 = s2.toupper ();

將" s5 "字符串(s5 = " GOODBYE ")轉(zhuǎn)換為全小寫(.tolower方法)

s4 = s5.tolower ( );

審核編輯：湯梓紅