LOGICAL Input: The L Descriptor

The Lw descriptor is used for LOGICAL input. The general form of the Lw descriptor is as follows:

The meaning of r and w are:

• L is for LOGICAL
• w is the width of field, which indicates that a LOGICAL value should be read in from the next w positions.
• In this w positions, the input should be in the following form: It starts with any number of spaces, followed by an optional period, followed by a T or F, followed by anything. The following are a few correct examples: .TRUE., TRUE, .TRUE, T, .T, Ten, Tennessee, .Ten dollars and .Ten. All of these input are equivalent to .TRUE. The following are a few other example, .FALSE., FALSE, .FALSE, .F., F, Four, .Fourteen, Florida, Fake, F.F.F. and FALSE_AND_TRUE. All of these input are equivalent to .FALSE. However, the following examples are all incorrect: Not_True (does not start with a T) and ..TRUE (starts with two periods).
• Consider the following example:

  LOGICAL :: a, b, c
  
  READ(*,"(L3, L8, L10)")  a, b, c
  

  Suppose the input is the following:

           1    1    2
  ....5....0....5....0.
  Fax  Trust   Thursday
  

  Variable a takes the first three positions, which contain F, a and x. Thus, a receives .FALSE. since the first character is a F. Variable b takes the next 8 positions, which contain two spaces, T, r, u, s, t and a space. Since the first non-blank character is a T, b receives .TRUE. Variable c takes the next 10 positions, which contain two spaces, T, h, u, r, s, d, a and y. Therefore, c also receives .TRUE.
• If you system recognizes lower cases, as many systems do, T and t are the same, and F and f are the same.
• r is the repetition indicator, which gives the number of times the edit descriptor should be repeated. For example, 3L5 is equivalent to L5, L5, L5.