Reading and Writing text (formatted) files with F90

Output Statements
- F90 supports 2 output statements :
- Notice the different placements of the comma in the statements
- NOTE:
- The WRITE statement uses a device number to specify the output device
The "*" format string
- I have been using the default format string * so far
  (Mainly because I want to focus on other issues)
- The format string * will cause Fortran will use "default" printing (each type of variable will have its own default format)
  Example:

Taylor-made Format Strings

The format string in a print or write controls the manner printing the values
The syntax of a format string is:
A format-spec can be:

Format descriptors: (not exhaustive, most commonly used only)

`X`	one space
`/`	new line
`A`	one character (ASCII code)
`I#`	integer number, with "#" of digits (overflow is printed as ****)
`F#1.#2`	*fixed point* number notation, with "#1" characters (i.e., spaces to print) and "#2" digits precision
`E#1.#2`	*floating point* number notation, with "#1" characters and "#2" digits precision NOTE: the number printed will be "-0.xxxxxxE-xx". #2 determines the number od "x". Hence, #1 >= #2 + 7 to allow meaningful output !
`D#1.#2`	*Double precision float* number notation, with "#1" characters and "#2" digits precision NOTE: the number printed will be "-0.xxxxxxE-xx". #2 determines the number od "x". Hence, #1 >= #2 + 7 to allow meaningful output ! (I can't see any difference in behavior from E... :-))

Examples:

I5 xxx (5 digits integers) <---> 5 char F10.2 xxxxx.xx <--------> 10 char E15.6 0.xxxxxxE+xx <----> 6 char <-------------> 15 char

Example Program: (Demo above code)
- Prog file: click here
Preceeding Count:
- A format descriptor can be preceeded by a count
  The count " repeats " the given format descriptor
- Examples:

Repeating the last format descriptor

The last format descriptor (not format string ) is assumed to be repeated ad infinitum
This behavior is best illustrated with x

Example 1:

print '(F7.2, 4X, F7.2)', A, B, C, D, E ^^^^ ^^^^
is processed as: print '(F7.2, 4X, F7.2)', A, B print '(F7.2, 4X, F7.2)', C, D print '(F7.2, 4X, F7.2)', E

I.e.: (F7.2, 4X, F7.2) is repeated ad infinitum

Example 2:

print '(F7.2, 4X, (F7.2))', A, B, C, D, E

is processed as:
print '(F7.2, 4X, F7.2)', A, B print '(F7.2)', C print '(F7.2)', D print '(F7.2)', E

I.e.: (F7.2) is repeated ad infinitum

Example Program: (Demo above code)
- Prog file: click here

Tricks to print arrays and matrices in F90

Array elements can be written using an implicit loop statement in the PRINT or WRITE statement

Example: one-dimensional array

PRINT *, (A(i), i = 1, 3) is equavalent to: PRINT *, A(1), A(2), A(3)

Example: two-dimensional array

PRINT *, ( (A(i,j), i = 1, 3), j = 1, 3 ) is equavalent to: PRINT *, A(1,1), A(1,2), A(1,3), A(2,1), A(2,2), A(2,3),...

Example Program: (Demo above code)
- Prog file: click here

A trick to print a one-dimensional array into a table of 2 columns:

REAL, DIMENSION(10) :: A print '("Table form of A"/(2F8.2))', (A(i), i = 1, 10)

output looks like this:
Table form of A A(1) A(2) A(3) A(4) A(5) A(6) A(7) A(8) A(9) A(10)

(F8.2, 4X, F8.2) is repeated !!!

A trick to print a matrix :

REAL, DIMENSION(10, 10) :: A print '("Matrix A"/(10F8.2))', ((A(i,j), i = 1, 10), j = 1, 10)

output looks like this:
Matrix A A(1,1) A(1,2) A(1,3) A(1,4) A(1,5) ... A(2,1) A(2,2) ... A(3,1) A(3,2) ... A(4,1) A(4,2) ... .... A(10,1) A(10,2) ...

Example Program: (Demo above code)
- Prog file: click here

No NEWLINEThe PRINT will always print a newline To prevent a WRITE statement from advancing to the next lne , add ADVANCE="NO" as the third option in the format string Example: printing a matrix print *, "Matrix B" DO i = 1, N DO j = 1, N write (6, "(F8.2)", ADVANCE="NO") B(i, j) END DO print * END DO

Reading data from the terminal The input statement to read data from the terminal in F90 are: READ Format-String , Variables READ (5 , Format-String) Variables The terminal input is device 5 The form READ (5 , Format-String) ... is more flexible, because you can specify a specific device number Important note: Be aware that Fortran is record oriented (punch cards !) The format string is used to denote the size of a record field Example: INTEGER A READ (5, "(I3)" ) A ! reads a 3 digit integer Example Program: (Demo above code) Prog file: click here Recommendation : always use the default format string in a READ statement: Use READ (dev# , *) Variables Example: INTEGER A READ (5 , *) A

File I/O A file is opened for input and output using the OPEN statement Syntax of the OPEN statement: OPEN( DeviceNumber, FILE='InputFileName' ) Example: OPEN( 10, FILE='myFile' ) Reading from the file: READ ( 10, Format-String ) Variables Writing to the file: WRITE ( 10, Format-String , [advance="NO"]) Variables Warning: Do not attempt to read and write to a file at the same time A write operation will append to the file and more the file access pointer to the end of the file A subsequent read operation will fail ... Example Program: (Demo above code) Prog file: click here Sample input: click here

Reading a Matrix from a file Example: PROGRAM main IMPLICIT NONE REAL, DIMENSION(4,4) :: B INTEGER i, j OPEN ( 10, FILE="inputMatrix" ) READ (10, *) ((B(i, j), i = 1, 4), j = 1, 4) END Example Program: (Demo above code) Prog file: click here Input matrix file: click here

Closing a file After you finish writing a file , you must close the file to avoid possible data loss due to system loss of your data CLOSE(deviceNumber)
Random file access in Fortran ? Fortran does not seem to be able to access files randomly The only feature that I can find is it can rewind an opened file to the beginning - and the file can be read again from the start...
System calls in Fortran ? There is no uniform support for UNIX system calls in Fortran Some UNIX operating systems may provide system calls, others do not. Check with manufacturer....

`4X`	`XXXX`
`2I8`	`I8 I8`