/**
@page working_with_data_validation Working with Data Validation

@tableofcontents


Data validation is a feature of Excel which allows restrictions to be placed
on the data that a user enters in a cell and to display associated help and
warning messages. It can also be used to restrict input to values in a drop
down list.

A typical use case might be to restrict data in a cell to integer values in a
certain range, to provide a help message to indicate the required value and to
issue a warning if the input data doesn't meet the stated criteria. In
`libxlsxwriter` this can be done as follows:

@code

   lxw_data_validation *data_validation = calloc(1, sizeof(lxw_data_validation));

   data_validation->validate       = LXW_VALIDATION_TYPE_INTEGER;
   data_validation->criteria       = LXW_VALIDATION_CRITERIA_BETWEEN;
   data_validation->minimum_number = 1;
   data_validation->maximum_number = 10;

   worksheet_data_validation_cell(worksheet, CELL("B3"), data_validation);

@endcode

@image html data_validate1.png

If the user inputs a value that doesn't match the specified criteria an error
message is displayed:

@image html data_validate4.png


For more information on data validation see the Microsoft support article
[Description and examples of data validation in Excel](http://support.microsoft.com/kb/211485).

The following sections describe how to use the
`worksheet_data_validation_cell()` and `worksheet_data_validation_range()`
functions and the various options of #lxw_data_validation.


@section ww_data_validate_functions The data validation functions


The `worksheet_data_validation_cell()` and `worksheet_data_validation_range()`
functions are used to construct an Excel data validation.

The data validation can be applied to a single cell or a range of cells:

@code
   worksheet_data_validation_cell( worksheet, 2, 1,       data_validation);
   worksheet_data_validation_range(worksheet, 2, 1, 4, 1, data_validation);

   // Same as above using the CELL() and RANGE() macros.
   worksheet_data_validation_cell( worksheet, CELL("B3"),     data_validation);
   worksheet_data_validation_range(worksheet, RANGE("B3:B5"), data_validation);

@endcode

The lxw_data_validation struct used in these functions is explained below.


@section ww_data_validate_struct The lxw_data_validation struct

The lxw_data_validation struct is used to set the properties of a data
validation. A typical usage would look something like this:

@code
    lxw_data_validation *data_validation = calloc(1, sizeof(lxw_data_validation));
    data_validation->validate     = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria     = LXW_VALIDATION_CRITERIA_GREATER_THAN;
    data_validation->value_number = 10;
    data_validation->show_input   = LXW_VALIDATION_OFF;
@endcode

This example shows the main properties of lxw_data_validation and Excel data
validations:

- `validate`: The type of data to restrict the validation to. In this case it
  is whole numbers.

- `criteria`: The criteria by which the data will be evaluated. In this case
  whether the input is greater than a value.

- `value`: The value that the criteria applies to. This has several different
  versions for different types of data. This could also be a `minimum` and
  `maximum` value if the criteria used is a "BETWEEN" criteria. This is
  explained in the @ref ww_data_validate_value section below.

- Other options such as `show_input` or `input_message`. These parameters are
  explained in the @ref ww_data_validate_options section.

Note, in the examples in this document the `data_validation` variable is shown
as dynamically allocated, however an address of a static or automatic variable
could also be used. In these cases make sure that the struct members are
initialized to zero before setting other parameters.

@subsection ww_data_validate_validate validate

The `validate` parameter is used to set the type of data that you wish to
validate:

@code
    data_validation->validate = LXW_VALIDATION_TYPE_INTEGER;
@endcode

It is always required and it has no default value. In Excel the validate
parameters are:

- Whole
- Decimal
- List
- Date
- Time
- Text Length
- Custom
- Any

The equivalent parameters in libxlsxwriter are defined in
#lxw_validation_types:

 - #LXW_VALIDATION_TYPE_INTEGER: Restrict cell input to whole/integer numbers
   only.

 - #LXW_VALIDATION_TYPE_INTEGER_FORMULA: Restrict cell input to whole/integer
   numbers only, using a cell reference.

 - #LXW_VALIDATION_TYPE_DECIMAL: Restrict cell input to decimal numbers only.

 - #LXW_VALIDATION_TYPE_DECIMAL_FORMULA: Restrict cell input to decimal
   numbers only, using a cell reference.

 - #LXW_VALIDATION_TYPE_LIST: Restrict cell input to a list of strings in a
   dropdown.

 - #LXW_VALIDATION_TYPE_LIST_FORMULA: Restrict cell input to a list of strings
   in a dropdown, using a cell range.

 - #LXW_VALIDATION_TYPE_DATE: Restrict cell input to date values only, using a
   lxw_datetime type.

 - #LXW_VALIDATION_TYPE_DATE_FORMULA: Restrict cell input to date values only,
   using a cell reference.

 - #LXW_VALIDATION_TYPE_TIME: Restrict cell input to time values only, using a
   lxw_datetime type.

 - #LXW_VALIDATION_TYPE_TIME_FORMULA: Restrict cell input to time values only,
   using a cell reference.

 - #LXW_VALIDATION_TYPE_LENGTH: Restrict cell input to strings of defined
   length, using a cell reference.

 - #LXW_VALIDATION_TYPE_LENGTH_FORMULA: Restrict cell input to strings of
   defined length, using a cell reference.

 - #LXW_VALIDATION_TYPE_CUSTOM_FORMULA: Restrict cell to input controlled by a
   custom formula that returns `TRUE/FALSE`.

 - #LXW_VALIDATION_TYPE_ANY: Allow any type of input. Mainly only useful for
   pop-up messages.



@subsection ww_data_validate_criteria criteria

The `criteria` parameter is used to set the criteria by which the data in the
cell is validated. It is almost always required except for the `list`,
`custom` and `any` validate options. It has no default value:

@code
    data_validation->criteria = LXW_VALIDATION_CRITERIA_GREATER_THAN;
@endcode


Allowable values are defined in #lxw_validation_criteria:

- #LXW_VALIDATION_CRITERIA_BETWEEN: Select data between two values.

- #LXW_VALIDATION_CRITERIA_NOT_BETWEEN: Select data that is not between two values.

- #LXW_VALIDATION_CRITERIA_EQUAL_TO: Select data equal to a value.

- #LXW_VALIDATION_CRITERIA_NOT_EQUAL_TO: Select data not equal to a value.

- #LXW_VALIDATION_CRITERIA_GREATER_THAN: Select data greater than a value.

- #LXW_VALIDATION_CRITERIA_LESS_THAN: Select data less than a value.

- #LXW_VALIDATION_CRITERIA_GREATER_THAN_OR_EQUAL_TO: Select data greater than or equal to a value.

- #LXW_VALIDATION_CRITERIA_LESS_THAN_OR_EQUAL_TO: Select data less than or equal to a value.


The `list`, `custom` and `any` validate options don't require a
`criteria`. If you specify one it will be ignored.


@subsection ww_data_validate_value value, minimum, maximum

The `value` parameters are used to set the limiting value to which the
`criteria` is applied. It is always required and it has no default
value. There are different types of `value` parameter associated with
different types of data. They are:

`value_number`:

The `value_number` parameter is used to set the limiting value
to which the criteria is applied using a whole or decimal number. It is
typically used with #LXW_VALIDATION_TYPE_INTEGER and
#LXW_VALIDATION_TYPE_DECIMAL and #LXW_VALIDATION_TYPE_LENGTH.

@code
    data_validation->validate     = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria     = LXW_VALIDATION_CRITERIA_GREATER_THAN;
    data_validation->value_number = 0;

    data_validation->validate     = LXW_VALIDATION_TYPE_DECIMAL;
    data_validation->criteria     = LXW_VALIDATION_CRITERIA_GREATER_THAN;
    data_validation->value_number = 10.5;

    data_validation->validate     = LXW_VALIDATION_TYPE_LENGTH;
    data_validation->criteria     = LXW_VALIDATION_CRITERIA_GREATER_THAN;
    data_validation->value_number = 3;
@endcode


`value_formula`:

The `value_formula` parameter is used to set the limiting value to which the
criteria is applied using a cell reference. It is valid for any of the
#lxw_validation_types types that end in `_FORMULA`:

@code
    data_validation->validate      = LXW_VALIDATION_TYPE_INTEGER_FORMULA;
    data_validation->criteria      = LXW_VALIDATION_CRITERIA_GREATER_THAN;
    data_validation->value_formula = "=E3";

    data_validation->validate      = LXW_VALIDATION_TYPE_TIME_FORMULA;
    data_validation->criteria      = LXW_VALIDATION_CRITERIA_EQUAL;
    data_validation->value_formula = "=H1";

    data_validation->validate      = LXW_VALIDATION_TYPE_LIST_FORMULA;
    data_validation->value_formula = "=$E$4:$G$4";
@endcode

`value_list`:

The `value_list` parameter is used to set a list of strings for a drop down
list.  The list should be a `NULL` terminated array of char* strings:

@code
    char *list[] = {"open", "high", "close", NULL};

    data_validation->validate   = LXW_VALIDATION_TYPE_LIST;
    data_validation->value_list = list;
@endcode

Note, when using the #LXW_VALIDATION_TYPE_LIST validation with a list of
strings, like in the last example above, Excel stores the strings internally
as a Comma Separated Variable string. The total length for this string,
including commas, cannot exceed the Excel limit of 255 characters. For longer
sets of data you should use a range reference like the previous example above.

`value_datetime`:

The `value_datetime` parameter is used to set the limiting value to which the
#LXW_VALIDATION_TYPE_DATE or #LXW_VALIDATION_TYPE_TIME criteria is applied
using a #lxw_datetime struct:

@code
    lxw_datetime datetime1          = {2017,  9,  24,  0,  0, 0};
    lxw_datetime datetime2          = {   0,  0,   0, 12, 30, 0};

    data_validation->validate       = LXW_VALIDATION_TYPE_DATE;
    data_validation->criteria       = LXW_VALIDATION_CRITERIA_EQUAL;
    data_validation->value_datetime = datetime1;

    data_validation->validate       = LXW_VALIDATION_TYPE_TIME;
    data_validation->criteria       = LXW_VALIDATION_CRITERIA_EQUAL;
    data_validation->value_datetime = datetime2;
@endcode

The `minimum` and `maximum` parameters are used to set the lower and upper
limiting values when the `criteria` is either #LXW_VALIDATION_CRITERIA_BETWEEN
or #LXW_VALIDATION_CRITERIA_NOT_BETWEEN. The parameters are:

- `minimum_number`
- `minimum_formula`
- `minimum_datetime`
- `maximum_number`
- `maximum_formula`
- `maximum_datetime`

They are similar to the `value` parameters described above. For example:

@code
    data_validation->validate         = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_number   = 1;
    data_validation->maximum_number   = 10;

    data_validation->validate         = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_NOT_BETWEEN;
    data_validation->minimum_formula  = "=E3";
    data_validation->maximum_formula  = "=F3";

    data_validation->validate         = LXW_VALIDATION_TYPE_DATE;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_datetime = datetime1;
    data_validation->maximum_datetime = datetime2;
@endcode

@section ww_data_validate_options Data validation options


@subsection ww_data_validate_ignore_blank ignore_blank


The `ignore_blank` parameter is used to toggle on and off the 'Ignore blank'
option in the Excel data validation dialog. When the option is on the data
validation is not applied to blank data in the cell. It is on by default:

@code
    data_validation->validate       = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria       = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_number = 1;
    data_validation->maximum_number = 10;
    data_validation->ignore_blank   = LXW_VALIDATION_OFF;
@endcode


@subsection ww_data_validate_dropdown dropdown

The `dropdown` parameter is used to toggle on and off the 'In-cell dropdown'
option in the Excel data validation dialog. When the option is on a dropdown
list will be shown for `list` validations. It is on by default.

@code
    data_validation->validate   = LXW_VALIDATION_TYPE_LIST;
    data_validation->value_list = list;
    data_validation->dropdown   = LXW_VALIDATION_OFF;
@endcode


@subsection ww_data_validate_input_title input_title

The `input_title` parameter is used to set the title of the input message that
is displayed when a cell is entered. It has no default value and is only
displayed if the input message is also displayed. See the `input_message`
parameter below.

The maximum title length is 32 characters.


@subsection ww_data_validate_input_message input_message

The `input_message` parameter is used to set the input message that is
displayed when a cell is entered. It has no default value:

@code
    data_validation->validate       = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria       = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_number = 1;
    data_validation->maximum_number = 100;
    data_validation->input_title    = "Enter an integer:";
    data_validation->input_message  = "between 1 and 100";
@endcode

The input message generated from the above example is:

@image html data_validate3.png

The message can be split over several lines using newlines. The maximum message
length is 255 characters.


@subsection ww_data_validate_show_input show_input

The `show_input` parameter is used to toggle on and off the 'Show input
message when cell is selected' option in the Excel data validation dialog.
When the option is off an input message is not displayed even if it has been
set using `input_message`. It is on by default.


@subsection ww_data_validate_error_title error_title

The `error_title` parameter is used to set the title of the error message
that is displayed when the data validation criteria is not met. The default
error title is 'Microsoft Excel'. The maximum title length is 32 characters.


@subsection ww_data_validate_error_message error_message

The `error_message` parameter is used to set the error message that is
displayed when a cell is entered. The default error message is "The value you
entered is not valid. A user has restricted values that can be entered into
the cell". A non-default error message can be displayed as follows:

@code
    data_validation->validate       = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria       = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_number = 1;
    data_validation->maximum_number = 100;
    data_validation->input_title    = "Enter an integer:";
    data_validation->input_message  = "between 1 and 100";
    data_validation->error_title    = "Input value is not valid!";
    data_validation->error_message  = "It should be an integer between 1 and 100";
@endcode

Which give the following message:

@image html data_validate2.png

The message can be split over several lines using newlines. The maximum message
length is 255 characters.


@subsection ww_data_validate_error_type error_type

The `error_type` parameter is used to specify the type of error dialog that is
displayed. There are 3 #lxw_validation_error_types options:

- #LXW_VALIDATION_ERROR_TYPE_STOP, the default.
- #LXW_VALIDATION_ERROR_TYPE_WARNING
- #LXW_VALIDATION_ERROR_TYPE_INFORMATION

@subsection ww_data_validate_show_error show_error

The `show_error` parameter is used to toggle on and off the 'Show error alert
after invalid data is entered' option in the Excel data validation dialog.
When the option is off an error message is not displayed even if it has been
set using `error_message`. It is on by default.

@section ww_data_validate_examples Examples

@code
    // Restrict input to an integer between 1 and 10.
    data_validation->validate         = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_number   = 1;
    data_validation->maximum_number   = 10;

    // Restrict input to an integer not between 1 and 10 (using cell references).
    data_validation->validate         = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_NOT_BETWEEN;
    data_validation->minimum_formula  = "=E3";
    data_validation->maximum_formula  = "=F3";

    // Restrict input to a decimal between 0.1 and 0.5.
    data_validation->validate         = LXW_VALIDATION_TYPE_DECIMAL;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_number   = 0.1;
    data_validation->maximum_number   = 0.5;

    // Select a value from a drop down list.
    char *list[]                      = {"open", "high", "close", NULL};

    data_validation->validate         = LXW_VALIDATION_TYPE_LIST;
    data_validation->value_list       = list;

    // Select a value from a drop down list (using a cell range).
    data_validation->validate         = LXW_VALIDATION_TYPE_LIST;
    data_validation->value_formula    = "=$E$4:$G$4";

    // Restrict input to a date between 1/1/2008 and 12/12/2008.
    lxw_datetime datetime1            = {2008,  1,  1, 0, 0, 0};
    lxw_datetime datetime2            = {2008, 12, 12, 0, 0, 0};

    data_validation->validate         = LXW_VALIDATION_TYPE_DATE;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_datetime = datetime1;
    data_validation->maximum_datetime = datetime2;

    // Restrict input to a string longer than 3 characters.
    data_validation->validate         = LXW_VALIDATION_TYPE_LENGTH;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_GREATER_THAN;
    data_validation->value_number     = 3;

    // Restrict input to a value if a formula is true.
    data_validation->validate         = LXW_VALIDATION_TYPE_CUSTOM_FORMULA;
    data_validation->value_formula    = "=AND(F5=50,G5=60)";

    // Display a custom info message when integer isn't between 1 and 100.
    data_validation->validate         = LXW_VALIDATION_TYPE_INTEGER;
    data_validation->criteria         = LXW_VALIDATION_CRITERIA_BETWEEN;
    data_validation->minimum_number   = 1;
    data_validation->maximum_number   = 100;
    data_validation->input_title      = "Enter an integer:";
    data_validation->input_message    = "between 1 and 100";
    data_validation->error_title      = "Input value is not valid!";
    data_validation->error_message    = "It should be an integer between 1 and 100";
@endcode

For a full example see @ref data_validate.c.

Next: @ref working_with_conditional_formatting

*/