Added utility string conversion function

src/grib_api_prototypes.h

@@ -1470,6 +1470,7 @@ int strcmp_nocase(const char *s1, const char *s2);
 void rtrim(char *s);
 const char *extract_filename(const char *filepath);
 char **string_split(char *inputString, const char *delimiter);
+int string_to_long(const char* input, long* output);
 
 /* functions.c */
 long grib_op_eq(long a, long b);

src/string_util.c

@@ -91,3 +91,28 @@ char** string_split(char* inputString, const char* delimiter)
 
     return result;
 }
+
+/* Return 0 if can convert input to an integer, 1 otherwise */
+int string_to_long(const char* input, long* output)
+{
+    const int base = 10;
+    char *endptr;
+    errno = 0;
+    long val = 0;
+
+    if (!input) return 1;
+
+    val = strtol(input, &endptr, base);
+    if ( (errno == ERANGE && (val == LONG_MAX || val == LONG_MIN)) ||
+         (errno != 0 && val == 0) )
+    {
+        //perror("strtol");
+        return 1;
+    }
+    if (endptr == input) {
+        //fprintf(stderr, "No digits were found. EXIT_FAILURE\n");
+        return 1;
+    }
+    *output = val;
+    return 0; // OK
+}