Add isnumeric function.

1 files changed, 32 insertions, 0 deletions

diff --git a/doc/gawktexi.in b/doc/gawktexi.in
index 37ecbc9f..81a24079 100644
--- a/doc/gawktexi.in
+++ b/doc/gawktexi.in
@@ -803,6 +803,8 @@ particular records in a file and perform operations upon them.
                                         once.
 * Shell Quoting::                       A function to quote strings for the
                                         shell.
+* Isnumeric Function::                  A function to test whether a value
+                                        is numeric.
 * Data File Management::                Functions for managing command-line
                                         data files.
 * Filetrans Function::                  A function for handling data file
@@ -21374,6 +21376,7 @@ programming use.
 * Getlocaltime Function::       A function to get formatted times.
 * Readfile Function::           A function to read an entire file at once.
 * Shell Quoting::               A function to quote strings for the shell.
+* Isnumeric Function::          A function to test whether a value is numeric.
 @end menu
 
 @node Strtonum Function
@@ -22164,6 +22167,35 @@ function shell_quote(s,             # parameter
 @c endfile
 @end example
 
+@node Isnumeric Function
+@subsection Checking whether a value is numeric
+
+A frequent programming question is how to ascertain whether a value is numeric.
+This can be solved by using this example function @code{isnumeric()}, which
+employs the trick of converting a string value to user input by using the
+@code{split()} function:
+
+@cindex @code{isnumeric()} user-defined function
+@cindex user-defined @subentry function @subentry @code{isnumeric()}
+@example
+@c file eg/lib/isnumeric.awk
+# isnumeric --- check whether a value is numeric
+
+function isnumeric(x,  f)
+@{
+	switch (typeof(x)) @{
+	case "strnum":
+	case "number":
+		return 1
+	case "string":
+		return (split(x, f, " ") == 1) && (typeof(f[1]) == "strnum")
+	default:
+		return 0
+	@}
+@}
+@c endfile
+@end example
+
 @node Data File Management
 @section @value{DDF} Management