Fortran is a very old programming language, but it has always played a very important role in scientific calculation and engineering calculation. Format statement is an important part of fortran, which allows programmers to control the output format and is very flexible and convenient. This paper will introduce the format statements in fortran and their usage and application.
Grammar of format statement
In fortran, the use of format statements needs to follow certain grammatical rules. The following is a common format:
Format ([format control statement] [,format control statement] ...)
Most extentsion syntax, such as using header field, is optional in format statement, but using guide field is mandatory. In the previous syntax, square brackets indicate options, and ellipsis indicates items that are allowed to be repeated many times.
Comment field of format statement
In fortranformat statements, the comment field is an option to record additional information. A comment field usually contains the following information:
Type of format item
Filling of spaces and zeros
Width and accuracy
The comment field can be used to process input and output, and can also be used for data formatting during file access. The following is an example of the print format of the comment field:
Sample _ Procedure.f90
Program Format _ Example
Implied nothing
integer，parameter::WP = selected _ real _ kind(8，99)
Real number (wp):: pi
Integer, parameter:: n=50
pi=4.0_wp*atan( 1.0_wp)
Write (*, "(a, i4, f10.8)") "The Valueofpiwith", n, "significantdigitsis differentiation:", pi.
endprogramformat_example
The output of the above program is as follows:
The value of 50 significant digits is: 3. 14 159265.
In the above code, the comment field "a" is followed by a string "Thevalueofpiwith", which we call a character conversion descriptor, which explains the type of fortran output format. Followed by "i4" indicates the width information. The remaining "f 10.8" represents the real output format of fortran.
Other fields of the format declaration
In fortran, there are many other format control fields that can be used, including exponential descriptors (e, es, d, etc.). ), hexadecimal format descriptors and other more specialized types.
The following are examples of using different descriptors:
Sample _ Procedure.f90
Program Format _ Example
Recessive ketone
integer，parameter::WP = selected _ real _ kind(8，99)
Real number (wp):: pi
Integer, parameter:: n=50
pi=4.0_wp*atan( 1.0_wp)
Write (*, "(a, i4, 2x, f 10.8, 2x, f 10.3, 2x, e 12.7)")"Piwith", n
, "significant figures:", pi, pi, pi.
endprogramformat_example
The output of the above program is as follows:
Piwith 50 Valid digits: 3.141592653.142 e+00.
In the above code, we used three different output format selectors: f 10.8, f 10.3 and e 12.7. Where f stands for real number type, 10.8 stands for output width and precision, and e stands for exponential type (scientific counting method), and the output width (12) and the number of digits reserved for precision are also specified.
Application of format statement
Format statement in Fortran can be used in various occasions, including printing screen output, writing text files, and even data formatting operations of binary files. Suppose we want to write the following program into a text file:
Sample _ Procedure.f90
Program Format _ Example 2
Recessive ketone
Integers:: I, J, K.
doi= 1， 10，2
doj= 1，5， 1
k=i+j
Write (*, "(3i5)")i, J, K.
Endor
Endor
endprogramformat_example2
The output of the above program is as follows:
% format example
1 12
123
134
145
156
3 14
325
336
347
358
5 16
527
538
549
55 10
In the above code, we used the 3i5 option, which means "3 integers with a bit width of 5", that is, for each cycle, we printed I, J and K as integers with a bit width of 5.
abstract
Format statement plays an important role in fortran, which can help us control the format of program output and make our output more reasonable and readable. In addition, the format statement can also be used for data access (input/output) and file formatting operations. I hope this article can help you better master the format statements in fortran.