Fortran字串


Fortran語言可以把字元作為單個字元或連續的字串。

字串可以是只有一個長度的字元,或者它甚至可以是零長度。在Fortran語言,字元常數是一對雙引號或單引號之間字元內容。

內部資料型別的字元儲存字元和字串。字串的長度可以通過len個符來指定。如果沒有指定長度,它是長度是1. 可以將字串按位元置指的是指在單個字元;最左邊的字元的位置是1。

字串宣告

宣告一個字串跟其他變數是一樣的:

type-specifier :: variable_name

例如,

Character(len=20) :: firstname, surname

可以指定一個值類似,

character (len=40) :: name  
name = Zara Ali

下面的例子演示了宣告和使用字元資料型別:

program hello
implicit none

   character(len=15) :: surname, firstname 
   character(len=6) :: title 
   character(len=25)::greetings
   
   title = 'Mr.' 
   firstname = 'Rowan' 
   surname = 'Atkinson'
   greetings = 'A big hello from Mr. Beans'
   
   print *, 'Here is', title, firstname, surname
   print *, greetings
   
end program hello

當編譯並執行上述程式,將產生以下結果:

Here is Mr. Rowan Atkinson       
A big hello from Mr. Bean

字串連線

連線運算子//,連線字串。

下面的例子說明了這一點:

program hello
implicit none

   character(len=15) :: surname, firstname 
   character(len=6) :: title 
   character(len=40):: name
   character(len=25)::greetings
   
   title = 'Mr.' 
   firstname = 'Rowan' 
   surname = 'Atkinson'
   
   name = title//firstname//surname
   greetings = 'A big hello from Mr. Beans'
   
   print *, 'Here is', name
   print *, greetings
   
end program hello

當編譯並執行上述程式,將產生以下結果:

Here is Mr. Rowan Atkinson       
A big hello from Mr. Bean

提取子串

在Fortran中,可以通過索引的字串,開始和子串一對括號的結束索引,從字串中提取一個子字串。這就是所謂的範圍說明。

下面的範例顯示了如何提取字串'Hello World'的子字串“world”:

program subString

   character(len=11)::hello
   hello = "Hello World"
   print*, hello(7:11)
   
end program subString 

當編譯並執行上述程式,將產生以下結果:

World

例子

下面的範例使用 date_and_time 函式,得到日期和時間的字串。我們使用範圍說明符單獨提取年份,日期,月份,小時,分鐘和秒的資訊。

program  datetime
implicit none

   character(len = 8) :: dateinfo ! ccyymmdd
   character(len = 4) :: year, month*2, day*2

   character(len = 10) :: timeinfo ! hhmmss.sss
   character(len = 2)  :: hour, minute, second*6

   call  date_and_time(dateinfo, timeinfo)

   !  lets break dateinfo into year, month and day.
   !  dateinfo has a form of ccyymmdd, where cc = century, yy = year
   !  mm = month and dd = day

   year  = dateinfo(1:4)
   month = dateinfo(5:6)
   day   = dateinfo(7:8)

   print*, 'Date String:', dateinfo
   print*, 'Year:', year
   print *,'Month:', month
   print *,'Day:', day

   !  lets break timeinfo into hour, minute and second.
   !  timeinfo has a form of hhmmss.sss, where h = hour, m = minute
   !  and s = second

   hour   = timeinfo(1:2)
   minute = timeinfo(3:4)
   second = timeinfo(5:10)

   print*, 'Time String:', timeinfo
   print*, 'Hour:', hour
   print*, 'Minute:', minute
   print*, 'Second:', second   
   
end program  datetime

當編譯並執行上述程式,它提供了詳細的日期和時間資訊:

Date String: 20140803
   Year: 2014
   Month: 08
   Day: 03
   Time String: 075835.466
   Hour: 07
   Minute: 58
   Second: 35.466

字串修整

trim函式接受一個字串,並刪除所有尾隨空格後返回輸入字串。

例子

program trimString
implicit none

   character (len=*), parameter :: fname="Susanne", sname="Rizwan"
   character (len=20) :: fullname 
   
   fullname=fname//" "//sname !concatenating the strings
   
   print*,fullname,", the beautiful dancer from the east!"
   print*,trim(fullname),", the beautiful dancer from the east!"
   
end program trimString

當編譯並執行上述程式,將產生以下結果:

Susanne Rizwan, the beautiful dancer from the east!
Susanne Rizwan, the beautiful dancer from the east!

字串左右調整

函式 adjustl 需要一個字串,並通過去除前導空格,並追加其作為尾隨空白返回。

函式 adjustr 需要一個字串,並通過刪除尾隨空格和追加作為前導空格返回。

例子

program hello
implicit none

   character(len=15) :: surname, firstname 
   character(len=6) :: title 
   character(len=40):: name
   character(len=25):: greetings
   
   title = 'Mr. ' 
   firstname = 'Rowan' 
   surname = 'Atkinson'
   greetings = 'A big hello from Mr. Beans'
   
   name = adjustl(title)//adjustl(firstname)//adjustl(surname)
   print *, 'Here is', name
   print *, greetings
   
   name = adjustr(title)//adjustr(firstname)//adjustr(surname)
   print *, 'Here is', name
   print *, greetings
   
   name = trim(title)//trim(firstname)//trim(surname)
   print *, 'Here is', name
   print *, greetings
   
end program hello

當編譯並執行上述程式,將產生以下結果:

Here is Mr. Rowan  Atkinson           
A big hello from Mr. Bean
Here is Mr. Rowan Atkinson    
A big hello from Mr. Bean
Here is Mr.RowanAtkinson                        
A big hello from Mr. Bean

搜尋字串的子串

index 函式有兩個字串,並檢查是否第二個字串的第一個字串的子串。如果第二個引數是第一個引數的子字串,然後返回一個整數,是第一個字串第二個字串的開始索引,否則返回零。

例子

program hello
implicit none

   character(len=30) :: myString
   character(len=10) :: testString
   
   myString = 'This is a test'
   testString = 'test'
   
   if(index(myString, testString) == 0)then
      print *, 'test is not found'
   else
      print *, 'test is found at index: ', index(myString, testString)
   end if
   
end program hello

當編譯並執行上述程式,將產生以下結果:

test is found at index: 11