Runtime Character Type Conversion
Automatic conversion occurs between Ingres character string values and Pascal character string variables. There are four string-valued Ingres objects that can interact with character string variables. They are Ingres names, such as form and column names, database columns of type c, char, text or varchar, and form fields of type character. Several considerations apply when dealing with character string conversions, both to and from Ingres.
The conversion of Pascal character string variables used to represent Ingres names is simple: trailing blanks are truncated from the variables, because the blanks make no sense in that context. For example, the string literals "empform" and "empform" refer to the same form.
The conversion of other Ingres objects is a bit more complicated. First, the storage of character data in Ingres differs according to whether the medium of storage is a database column of type c or character, a database column of type text or varchar, or a character form field. Ingres pads columns of type c or character with blanks to their declared length. Conversely, it does not add blanks to the data in columns of type text or varchar, or in form fields.
Second, the storage of character data in Pascal differs according to whether the character variable is of fixed or varying length. The Pascal convention is to blank-pad fixed-length character strings, but not to pad varying-length character strings. For example, the character string "abc" coming from an Ingres object will be stored in a Pascal packed array[1..5] of char variable as the string "abc " followed by two blanks. However, the same string would be stored in a varying[5] of char variable as "abc" without any trailing blanks.
When retrieving character data from an Ingres database column or form field into a Pascal variable, you should always ensure that the variable is at least as long as the column or field, in order to avoid truncation of data.
Furthermore, take note of the following conventions:
• Data stored in a database column of type character is padded with blanks to the length of the column. The variable receiving such data, be it of fixed or varying length, will contain those blanks. Following Pascal rules, if a fixed-length variable is longer than the database column, the data retrieved into it is further padded with blanks to the length of the variable. In the case of a varying-length variable, no further padding takes place. If the variable is shorter than the database column, truncation of data occurs.
• Data stored in a database column of type text or varchar is not padded with blanks. If a fixed-length variable is longer than the data in the text or varchar column, when retrieved, the data is padded with blanks to the length of the variable. In the case of a varying-length variable, no padding takes place. If the variable is shorter than the database column, truncation of data occurs.
• Data stored in a character form field contains no trailing blanks. If a fixed-length variable is longer than the data in the field, when retrieved, the data is padded with blanks to the length of the variable. In the case of a varying-length variable, no padding takes place. If the variable is shorter than the field, truncation of data occurs.
When inserting character data into an Ingres database column or form field from a Pascal variable, note the following conventions:
• When data is inserted from a Pascal variable into a database column of type c or character and the column is longer than the variable, the column is padded with blanks. If the column is shorter than the variable, the data is truncated to the length of the column.
• When data is inserted from a Pascal variable into a database column of type text or varchar and the column is longer than the variable, no padding of the column takes place. Furthermore, by default, all trailing blanks in the data are truncated before the data is inserted into the text column. For example, when a string "abc" stored in a Pascal packed array[1..5] of char variable as "abc " is inserted into the text or varchar column, the two trailing blanks are removed and only the string "abc" is stored in the database column. To retain such trailing blanks, you can use the EQUEL notrim function. It has the following syntax:
notrim(stringvar)
where stringvar is a character string variable. An example demonstrating this feature follows later. When used with repeat queries, the notrim syntax is:
@notrim(stringvar)
If the text or varchar column is shorter than the variable, the data is truncated to the length of the column.
• When data is inserted from a Pascal variable into a character form field and the field is longer than the variable, no padding of the field takes place. In addition, all trailing blanks in the data are truncated before the data is inserted into the field. If the field is shorter than the data (even after all trailing blanks have been truncated), the data is truncated to the length of the field.
When comparing character data in an Ingres database column with character data in a Pascal variable, note the following convention:
• When comparing data in c, character, or varchar database columns with data in a character variable, all trailing blanks are ignored. Trailing blanks are significant in text. Initial or embedded blanks are significant in character, text, and varchar; they are ignored in c.
As described above, the conversion of character string data between Ingres objects and Pascal variables often involves the trimming or padding of trailing blanks, with resultant change to the data. If trailing blanks have significance in your application, give careful consideration to the effect of any data conversion. For information on the significance of blanks when comparing with various Ingres character types, see the QUEL Reference Guide.
The Ingres date data type is represented as a 25-byte character string.
The program fragment in the following example demonstrates the notrim function and the truncation rules explained above.
{
| Assume that a table called "textchar" has been created
| with the following CREATE statement:
|
| CREATE textchar
| (row = i4,
| data = text(10)) -- Note the text data type
}
## var
## row: Integer;
## p_data: packed array[1..7] of Char;
## v_data: varying[7] of Char;
...
p_data := 'abc '; {Holds "abc "}
v_data := 'abc'; {Holds "abc"}
{The following APPEND adds the string "abc" (blanks truncated)}
## append to textchar (#row = 1, #data = p_data)
{The following APPEND adds the string "abc" (never had blanks)}
## append to textchar (#row = 2, #data = v_data)
{
| This statement adds the string "abc ", with 4 trailing
| blanks left intact by using the NOTRIM function.
}
## append to textchar (#row = 3, #data = notrim(p_data))
{
| This RETRIEVE retrieves rows #1 and #2, because
| trailing blanks were suppressed when these rows were
| appended.
}
## retrieve (row = textchar.#row)
## where length (textchar.#data) = 3
## begin
writeln( 'row found = ', row );
## end;
{
| This RETRIEVE retrieves row #3, because the NOTRIM
| function left trailing blanks in the "data" variable
| in the last APPEND statement.
}
## retrieve (row = textchar.#row)
## where length (textchar.#data) = 7
## begin
writeln( 'row found = ', row );
## end;