utils: fix str(CDADA_E_FULL) overflow

Fix bug and make sure there is coverage for CDADA_E_COUNT in
test/utils.c.

Reported-by: CodexGPT-5.3 <noreply@openai.com>

Author: msune

CHANGELOG.md

@@ -9,6 +9,12 @@ Legend:
 - [O] Other
 ```
 
+### v0.6.4 ()
+
+- [B] utils: fix `cdada_strerr()` bounds handling for invalid and negative error codes
+- [B] utils: add missing human-readable message for `CDADA_E_FULL`
+- [O] tests: add coverage for `cdada_strerr()` valid, boundary and high invalid values
+
 ### v0.6.3 (28th January 2026)
 
 - [O] tests/CI: fixed compilation with GCC 16 (thanks A. Stieger). Added CI coverage for GCC 15.

src/utils.c

@@ -10,11 +10,12 @@ static const char* cdada_err_str[CDADA_E_COUNT] = {
 	"Out of memory",
 	"Feature unsupported",
 	"Empty",
-	"Incomplete"
+	"Incomplete",
+	"Full"
 };
 
 const char* cdada_strerr(int err){
-	return err >= CDADA_E_COUNT? "Invalid code" : cdada_err_str[err];
+	return (err < 0 || err >= CDADA_E_COUNT)? "Invalid code" : cdada_err_str[err];
 }
 
 const char* cdada_get_ver(){

test/combined_test.c

@@ -47,6 +47,12 @@ int main(int args, char** argv){
 	rv = cdada_stack_destroy(stack);
 	TEST_ASSERT(rv == CDADA_SUCCESS);
 
+	TEST_ASSERT(strcmp(cdada_strerr(CDADA_SUCCESS), "Success") == 0);
+	TEST_ASSERT(strcmp(cdada_strerr(CDADA_E_FULL), "Full") == 0);
+	TEST_ASSERT(strcmp(cdada_strerr(-1), "Invalid code") == 0);
+	TEST_ASSERT(strcmp(cdada_strerr(CDADA_E_COUNT), "Invalid code") == 0);
+	TEST_ASSERT(strcmp(cdada_strerr(CDADA_E_COUNT + 1000), "Invalid code") == 0);
+
 	//Add your test here, and return a code appropriately...
 	return rv == 0? EXIT_SUCCESS : EXIT_FAILURE;
 }