In this guide, we will discuss Fortran Strings. The Fortran language can treat characters as single character or contiguous strings.
A character string may be only one character in length, or it could even be of zero length. In Fortran, character constants are given between a pair of double or single quotes.
The intrinsic data type character stores characters and strings. The length of the string can be specified by len specifier. If no length is specified, it is 1. You can refer individual characters within a string referring by position; the left most character is at position 1.
String Declaration
Declaring a string is same as other variables −
type-specifier :: variable_name
For example,
Character(len = 20) :: firstname, surname
you can assign a value like,
character (len = 40) :: name name = “Zara Ali”
The following example demonstrates declaration and use of character data type −
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
When you compile and execute the above program it produces the following result −
Here isMr. Rowan Atkinson A big hello from Mr. Bean
String Concatenation
The concatenation operator //, concatenates strings.
The following example demonstrates this −
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
When you compile and execute the above program it produces the following result −
Here is Mr. Rowan Atkinson A big hello from Mr. Bean
Extracting Substrings
In Fortran, you can extract a substring from a string by indexing the string, giving the start and the end index of the substring in a pair of brackets. This is called extent specifier.
The following example shows how to extract the substring ‘world’ from the string ‘hello world’ −
program subString character(len = 11)::hello hello = "Hello World" print*, hello(7:11) end program subString
When you compile and execute the above program it produces the following result −
World
Example
The following example uses the date_and_time function to give the date and time string. We use extent specifiers to extract the year, date, month, hour, minutes and second information separately.
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) ! let’s 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 ! let’s 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
When you compile and execute the above program, it gives the detailed date and time information −
Date String: 20140803 Year: 2014 Month: 08 Day: 03 Time String: 075835.466 Hour: 07 Minute: 58 Second: 35.466
Trimming Strings
The trim function takes a string, and returns the input string after removing all trailing blanks.
Example
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
When you compile and execute the above program it produces the following result −
Susanne Rizwan , the beautiful dancer from the east! Susanne Rizwan, the beautiful dancer from the east!
Left and Right Adjustment of Strings
The function adjustl takes a string and returns it by removing the leading blanks and appending them as trailing blanks.
The function adjustr takes a string and returns it by removing the trailing blanks and appending them as leading blanks.
Example
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
When you compile and execute the above program it produces the following result −
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
Searching for a Substring in a String
The index function takes two strings and checks if the second string is a substring of the first string. If the second argument is a substring of the first argument, then it returns an integer which is the starting index of the second string in the first string, else it returns zero.
Example
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
When you compile and execute the above program it produces the following result −
test is found at index: 11
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