Preference in C between static const char *const and static const char []?

[niooss-ledger]

Hello,

While reading libsodium's code, I stumbled upon itoa64 in src/libsodium/crypto_pwhash/scryptsalsa208sha256/crypto_scrypt-common.c:

libsodium/src/libsodium/crypto_pwhash/scryptsalsa208sha256/crypto_scrypt-common.c

Lines 31 to 32 in a84a99a

	static const char *const itoa64 =
	"./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

I am wondering why the code was written with a pointer instead of a vector:

static const char itoa64[65] =
     "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

From my understanding, using a pointer makes the compiler create both a string and a pointer to it, which is less efficient than using the string directly. Nevertheless, when I checked the compiled code (when building for x86-64), the compiler only stored the string. I guess this is due to the fact the compiler was able to optimize uses of itoa64 to remove pointer dereferences (because of the second const in static const char *const itoa64).

Therefore, while the current code is fine, I am wondering whether it was a deliberate choice (or coding style) to use a pointer instead of a vector. Was there a reason to choose this way of defining itoa64?

[jedisct1]

Modern compilers optimize both to equivalent code. The pointer is eliminated even at the lowest optimization levels, since it is static and never modified.

This scrypt code was inherited from the original scrypt implementation by scrypt's author, and there's no functional reason to change it.

[niooss-ledger]

Thanks for the quick reply! Ok, I agree with you there is no functional reason to change the code.