XUtils string related updates

- allow count out-parameter of String_split() to be NULL
- introduce xStrndup()
- do not allow NULL pointers passed to String_eq()
  it is not used in any code
- implement String_startsWith(), String_contains_i() and String_eq()
  as inline header functions
- adjust several conversion issues

XUtils.h

@@ -9,6 +9,7 @@ in the source distribution for its full text.
 
 #include "config.h" // IWYU pragma: keep
 
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h> // IWYU pragma: keep
 #include <string.h> // IWYU pragma: keep
@@ -24,25 +25,31 @@ void* xCalloc(size_t nmemb, size_t size);
 
 void* xRealloc(void* ptr, size_t size);
 
-#define String_startsWith(s, match) (strncmp((s),(match),strlen(match)) == 0)
-#define String_contains_i(s1, s2) (strcasestr(s1, s2) != NULL)
-
 /*
  * String_startsWith gives better performance if strlen(match) can be computed
  * at compile time (e.g. when they are immutable string literals). :)
  */
+static inline bool String_startsWith(const char* s, const char* match) {
+   return strncmp(s, match, strlen(match)) == 0;
+}
+
+static inline bool String_contains_i(const char* s1, const char* s2) {
+   return strcasestr(s1, s2) != NULL;
+}
+
+static inline bool String_eq(const char* s1, const char* s2) {
+   return strcmp(s1, s2) == 0;
+}
 
 char* String_cat(const char* s1, const char* s2);
 
 char* String_trim(const char* in);
 
-int String_eq(const char* s1, const char* s2);
-
-char** String_split(const char* s, char sep, int* n);
+char** String_split(const char* s, char sep, size_t* n);
 
 void String_freeArray(char** s);
 
-char* String_getToken(const char* line, const unsigned short int numMatch);
+char* String_getToken(const char* line, unsigned short int numMatch);
 
 char* String_readLine(FILE* fd);
 
@@ -54,4 +61,6 @@ int xSnprintf(char *buf, int len, const char* fmt, ...);
 
 char* xStrdup(const char* str) ATTR_NONNULL;
 
+char* xStrndup(const char* str, size_t len) ATTR_NONNULL;
+
 #endif