New shared function, getenv_bool()

This provides a standard way to get a boolean from an environment
variable.  It treats the variable as true iff its value begins with 'y'
or 'Y', like most of the current implementations.  The function takes a
default value which it returns if the environment variable is undefined.

This replaces the various ad-hoc tests of environment variable scattered
around and mostly doesn't change their behaviour.  The exceptions are
TOWERS_2D in Towers and DEBUG_PUZZLES in the Windows front end.  Both of
those were treated as true if they were defined at all, but now follow
the same rules as other boolean environment variables.

1 files changed, 8 insertions, 0 deletions

diff --git a/misc.c b/misc.c
index c4c4b69..f18f17e 100644
--- a/misc.c
+++ b/misc.c
@@ -198,6 +198,14 @@ char *fgetline(FILE *fp)
     return ret;
 }
 
+bool getenv_bool(const char *name, bool dflt)
+{
+    char *env = getenv(name);
+    if (env == NULL) return dflt;
+    if (env[0] == 'y' || env[0] == 'Y') return true;
+    return false;
+}
+
 /* Utility functions for colour manipulation. */
 
 static float colour_distance(const float a[3], const float b[3])