workbook: add check for blank worksheet name

Issue #442

include/xlsxwriter/common.h

@@ -107,6 +107,9 @@ typedef enum lxw_error {
     /** Function parameter validation error. */
     LXW_ERROR_PARAMETER_VALIDATION,
 
+    /** Worksheet name cannot be blank. */
+    LXW_ERROR_SHEETNAME_IS_BLANK,
+
     /** Worksheet name exceeds Excel's limit of 31 characters. */
     LXW_ERROR_SHEETNAME_LENGTH_EXCEEDED,
 

include/xlsxwriter/workbook.h

@@ -469,6 +469,7 @@ lxw_workbook *workbook_new_opt(const char *filename,
  *
  * The worksheet name must be a valid Excel worksheet name, i.e:
  *
+ * - The name cannot be blank.
  * - The name is less than or equal to 31 UTF-8 characters.
  * - The name doesn't contain any of the characters: ` [ ] : * ? / \ `
  * - The name doesn't start or end with an apostrophe.
@@ -511,6 +512,7 @@ lxw_worksheet *workbook_add_worksheet(lxw_workbook *workbook,
  *
  * The chartsheet name must be a valid Excel worksheet name, i.e.:
  *
+ * - The name cannot be blank.
  * - The name is less than or equal to 31 UTF-8 characters.
  * - The name doesn't contain any of the characters: ` [ ] : * ? / \ `
  * - The name doesn't start or end with an apostrophe.
@@ -927,6 +929,7 @@ lxw_chartsheet *workbook_get_chartsheet_by_name(lxw_workbook *workbook,
  * This function is used to validate a worksheet or chartsheet name according
  * to the rules used by Excel:
  *
+ * - The name cannot be blank.
  * - The name is less than or equal to 31 UTF-8 characters.
  * - The name doesn't contain any of the characters: ` [ ] : * ? / \ `
  * - The name doesn't start or end with an apostrophe.

src/utility.c

@@ -40,6 +40,7 @@ char *error_strings[LXW_MAX_ERRNO + 1] = {
     "Feature is not currently supported in this configuration.",
     "NULL function parameter ignored.",
     "Function parameter validation error.",
+    "Worksheet name cannot be blank.",
     "Worksheet name exceeds Excel's limit of 31 characters.",
     "Worksheet name cannot contain invalid characters: '[ ] : * ? / \\'",
     "Worksheet name cannot start or end with an apostrophe.",

src/workbook.c

@@ -2607,6 +2607,11 @@ workbook_unset_default_url_format(lxw_workbook *self)
 lxw_error
 workbook_validate_sheet_name(lxw_workbook *self, const char *sheetname)
 {
+
+    /* Check for blank worksheet name. */
+    if (strlen(sheetname) == 0)
+        return LXW_ERROR_SHEETNAME_IS_BLANK;
+
     /* Check the UTF-8 length of the worksheet name. */
     if (lxw_utf8_strlen(sheetname) > LXW_SHEETNAME_MAX)
         return LXW_ERROR_SHEETNAME_LENGTH_EXCEEDED;

test/unit/workbook/test_workbook_validate_worksheet_name.c

@@ -145,3 +145,17 @@ CTEST(workbook, validate_worksheet_name09) {
 
     lxw_workbook_free(workbook);
 }
+
+/* Test for blank sheet name. */
+CTEST(workbook, validate_worksheet_name10) {
+
+    const char* sheetname = "";
+
+    lxw_workbook *workbook = workbook_new(NULL);
+    lxw_error exp = LXW_ERROR_SHEETNAME_IS_BLANK;
+    lxw_error got = workbook_validate_sheet_name(workbook, sheetname);
+
+    ASSERT_EQUAL(exp, got);
+
+    lxw_workbook_free(workbook);
+}