• HI everybody is there neway to read nth line from a data file in fortran 90 directly. That is i dont want to use do i=1,n-1 technique as my file is really long. Thanks in advsance! June 16, 2006, 10:03.
• An internal file to Fortran is simply a CHARACTER.n variable. Just give the name of the variable (it may be a substring if you wish) instead of the unit number in a Fortran READ or WRITE statement. Note that you must still write to a string and send the string to qprint or xvmessage.

FORTRAN Lesson 4 Reese Haywood Ayan Paul In Today’s lesson we will learn how to OPEN, READ and WRITE data les. I will then give you the tools necessary for tting a least squares line to set of data points. Finally, we will write a program that reads in a three column data le, nds the least squares staright-line t. routines in the fortran source like WATCOM Fortran 77 does?? (and read binary data files any amount at a time without. I would like to be able to read the last line of a (huge) input file without being compelled to read all of it: is there any way? I tried FSEEK but FORTRAN 77 does not like it. Thank you ahead lor. Ade, you have to know the length of the data before reading it into an array. This is a fundamental limitation of Fortran. If you have to read files of unknown length, you will have to read each file twice. Read a file once to determine the length, allocate the array, and then read in the data.

Sometimes it is convenient in a Fortran program to use files for accessing or storing data - especially when large amounts of data are involved. Too much keyboard input during the run of a program leads to mistakes and tedium, while too much screen output has similar consequences. Putting data into files - both for input and output - is a more leisurely and less error-prone approach.

Open

Fortran Read Statement

In place of number you insert a positive integer (but not 6) to be used to refer to the file, and instead of name you insert the name of the file. Here are examples of open commands:

Fortran uses the unit number to access the file with later read and write statements. Several files can be open at once, but each must have a different number. There is one thing to remember about numbering a file - you cannot use the number 6, as GNU Fortran reserves that number to refer to the screen.

Note that quotes enclose the filename. Also, in specifying a directory path for a file, you must use double backslashes instead of single ones. Do not put a space on either side of the colon after the drive letter. If you do not specify a drive or directory path for a file, or if you specify the same drive upon which GNU Fortran is installed but without a path, GNU Fortran will by default assume the file is located on the same drive and in the same directory from where Fortran is running.

If the named file does not already exist, Fortran will create it; if it does exist, Fortran will replace it. (So don't mistakenly give the file the same name as another important file!)

Close

The first of these commands closes the file numbered 5, while the second closes the three files numbered 1, 3, and 8. It is not necessary to close files; all files will automatically be closed when an end or stop statement is executed. However, in programs handling large amounts of data it can be prudent to close files before the end of the program in order to avoid possible memory problems and to increase efficiency.

Write (to Files)

works like a print * command, except that data is written to the file numbered 7 instead of to the screen. The two statements

produce exactly the same output, except that the first writes to the screen and the second to file number 7. The command 'write (7,*)' on a line by itself serves as a line feed, skipping a line in the file numbered 7 before the next writing to that file.

You can also use write statements in conjunction with format statements to write to a file; this gives you better control of formatting. In the following, the first number in 'write (7,5)' refers to the file number and the second to the label of the format statement:

The 'write (7,5)' command works exactly like the similar command 'write (*,5)', except that in the former output is directed to file number 7, and in the latter to the screen.

Each execution of a write command writes to a single line in a file. The next write command will write to a new line.

Here is a program that finds and prints to a file the divisors of an integer n :

Note that the program counts the divisors, storing them in an array d, until 10 are accumulated; then it prints these 10 on a single line, reserving 7 places for each divisor. It then begins a new count and repeats the procedure until all divisors are found. The last write statement prints whatever divisors are left over after the last full line of 10. The close statement, included here for demonstration only, is unnecessary, as the program is all but finished at that point and the end statement will automatically close the file anyway.

Read (from Files)

Fortran Read Line From File

Suppose for example that a file is numbered 7, and that the first two lines of the file contain the data (separated by commas)

If the first two read statements in the program are

Fortran Read Last Line From File Pdf

then the program assigns x = 1.23, y = 4.56, z = 7.89, m = 11, n = 13, first = 'Sally'. The variables will have to be declared in the program to correspond with the data assigned them by the read statements. For instance, in the above situation x, y, and z will have been declared real variables, m and n integers, and 'first' a character variable. Failure to match variable types with data types will most likely lead to error messages.

It is possible that a program does not know beforehand the length of a file. If data is being read from a loop, there is a way to exit the loop when all data in the file has been read, thereby avoiding a program hang-up. One simply modifies the read statement to something like

This command instructs Fortran to read the next line in the file numbered 7, but to jump to the statement labelled 10 in the program in the event that the last line in that file has already been read.

You can also use format specifiers in read statements, but this can be somewhat tedious and we will not go into the details. As but one example, suppose you want to make the assignments

where n is an integer and x and y are real variables. Then you may use the read and format statements

and in file number 7 place the corresponding line of data

Fortran Read Error

Fortran will read and separate the data, insert appropriate decimal points, and assign it to the variables. But as you can see the method is confusing and perhaps not worth the effort.

Fortran Read Last Line Of File

How to read values line by line AND count them?

How to read values line by line AND count them?