Declare many structures const (closes #3552)

Many structs used in mutt are actually constant but are defined
without the 'const' keyword. This can slow initialization (slightly)
in some environments due to extra copying and increases the amount of
writable RAM required at run-time, which can be significant on non-MMU
systems. Using const can also increase the opportunities for compiler
optimization.

The attached patch marks many such structures as const. On my test x86
build, this reduces the size of .data by over 50%.

1 files changed, 3 insertions, 3 deletions

diff --git a/mapping.h b/mapping.h
index 6f400575..760c33a8 100644
--- a/mapping.h
+++ b/mapping.h
@@ -21,12 +21,12 @@
 
 struct mapping_t
 {
-  char *name;
+  const char *name;
   int value;
 };
 
-char *mutt_getnamebyvalue (int, const struct mapping_t *);
-char *mutt_compile_help (char *, size_t, int, struct mapping_t *);
+const char *mutt_getnamebyvalue (int, const struct mapping_t *);
+char *mutt_compile_help (char *, size_t, int, const struct mapping_t *);
 
 int mutt_getvaluebyname (const char *, const struct mapping_t *);