String literals vs const char* in C

Question

Why don\'t ANSI C compilers flag the use of a string literal argument in a function call in which the correponding parameter does not have a const qualifier? For example,

Answer 1

gcc: Use the flag -Wwrite-strings

PS. gcc manual explains why this isn't part of -Wall. Anyway, as always, you should find a combination of -W flags that suits your particular needs and coding style. For example, in a recent project I have used something like this: -Werror -Wall -Wextra -Wformat=2 -Winit-self -Wswitch-enum -Wstrict-aliasing=2 -Wundef -Wshadow -Wpointer-arith -Wbad-function-cast -Wcast-qual -Wcast-align -Wwrite-strings -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -Wnested-externs -Winline -Wdisabled-optimization -Wunused-macros -Wno-unused

Answer 2

It is a K&R legacy. Fixing it would break a million programs.

Answer 3

The GNU compiler (and the Intel C compiler as well, iirc) will emit a warning, if -Wwrite-string is used:

$ gcc -Wall -Wwrite-strings -o foo /tmp/foo.c
/tmp/foo.c: In function 'main':
/tmp/foo.c:12: warning: passing argument 1 of 'somefunc' discards qualifiers from pointer target type
/tmp/foo.c:3: note: expected 'char *' but argument is of type 'const char *'

Concerning VS2010, I can't help you.

Answer 4

What Hans Passant said. const was added as part of the ANSI standard on 1989, so anything from before that didn't have const.

Answer 5

string literals are not const in C; in C++ they are.

edit: to clear up any confusion about my comment, I am referring to the type, not the ability to actually change them.