Fix ArmClang compiling error: isdigit()

Signed-off-by: Alamy Liu <alamy.liu@gmail.com>

tiny-json.c

@@ -2,7 +2,7 @@
 /*
 
 <https://github.com/rafagafe/tiny-json>
-     
+
   Licensed under the MIT License <http://opensource.org/licenses/MIT>.
   SPDX-License-Identifier: MIT
   Copyright (c) 2016-2018 Rafa Garcia <rafagarcia77@gmail.com>.
@@ -24,7 +24,7 @@
   LIABILITY, WHETHER IN AN ACTION OF  CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
   SOFTWARE.
-    
+
 */
 
 #include <string.h>
@@ -245,7 +245,7 @@ static char* nullValue( char* ptr, json_t* property ) {
   * @retval Null pointer if any error occur. */
 static char* expValue( char* ptr ) {
     if ( *ptr == '-' || *ptr == '+' ) ++ptr;
-    if ( !isdigit( *ptr ) ) return 0;
+    if ( !isdigit( (int)(*ptr) ) ) return 0;
     ptr = goNum( ++ptr );
     return ptr;
 }
@@ -255,7 +255,7 @@ static char* expValue( char* ptr ) {
   * @retval Pointer to first non numerical after the string. If success.
   * @retval Null pointer if any error occur. */
 static char* fraqValue( char* ptr ) {
-    if ( !isdigit( *ptr ) ) return 0;
+    if ( !isdigit( (int)(*ptr) ) ) return 0;
     ptr = goNum( ++ptr );
     if ( !ptr ) return 0;
     return ptr;
@@ -269,12 +269,12 @@ static char* fraqValue( char* ptr ) {
   * @retval Null pointer if any error occur. */
 static char* numValue( char* ptr, json_t* property ) {
     if ( *ptr == '-' ) ++ptr;
-    if ( !isdigit( *ptr ) ) return 0;
+    if ( !isdigit( (int)(*ptr) ) ) return 0;
     if ( *ptr != '0' ) {
         ptr = goNum( ptr );
         if ( !ptr ) return 0;
     }
-    else if ( isdigit( *++ptr ) ) return 0;
+    else if ( isdigit( (int)(*++ptr) ) ) return 0;
     property->type = JSON_INTEGER;
     if ( *ptr == '.' ) {
         ptr = fraqValue( ++ptr );
@@ -440,7 +440,7 @@ static char* goBlank( char* str ) {
   * @return The final pointer value or null pointer if the null character was found. */
 static char* goNum( char* str ) {
     for( ; *str != '\0'; ++str ) {
-        if ( !isdigit( *str ) )
+        if ( !isdigit( (int)(*str) ) )
             return str;
     }
     return 0;