![]() This way, AmountMonthAfter can also be calculated. When the second table is created, the first table tmp1Amounts is dropped using a Drop Table statement.įinally, a third pass is made through the data, but now with the months sorted in reverse order. By comparing the product on the current row with the product on the previous row, this condition can be validated. The If() function is needed since the AmountMonthBefore only should be calculated if the previous row contains the data for the same product but for the previous month. It orders the records first by product, then by month in ascending order. This is done by running a second pass through the data creating a new table tmp2Amounts. The initial table is sorted according to month, which means that the peek() function would in many cases return the amount for the wrong product. If(Product=Peek(Product),Peek(Amount)) as AmountMonthAfter If(Product=Peek(Product),Peek(Amount)) as AmountMonthBefore By using temporary tables and running multiple passes through the data, such problems can be avoided. Furthermore, the Peek() function cannot be used to reference data that has not yet been loaded. Example 4ĭata needs to be correctly sorted in order to get the correct results but, unfortunately, this is not always the case. Peek(Amount,2) returns the third value in the table: 7. By substituting this value, values of other rows in the table can be fetched: Using -1 as row_no means that the value from previous row will be used. In this example, the following three function calls are equivalent: Here, the row_no and table_name parameters are omitted, so the default values are used. The field AmountMonthBefore will hold the amount from the previous month. QIODevice uses these functions to implement all its convenience functions, such as getChar(), readLine() and write(). ![]() Subclasses of QIODevice are only required to implement the protected readData() and writeData() functions. To see the result, add the fields listed in the results column to a sheet in your app. By subclassing QIODevice, you can provide the same interface to your own I/O devices. If you want to access data further down in a table, you need to do it in two steps: first, load the entire table into a temporary table, and then re-sort it when using Peek().Īdd the example script to your app and run it. However, note that without specifying the table as the third argument table_name in these examples, the function references the current (in this case, internal) table. Peek('EmployeeCode',2, 'EmployeeDates') returns the third value, 103, in the table as the FirstCode. Substituting the value of the argument row_no returns the values of other rows in the table, as follows: LastCode = 106 because Peek('EmployeeCode',-1, 'EmployeeDates') returns the last value of EmployeeCode in the table EmployeeDates. It would make sense to heed the aforementioned warning and just not worry what it does.FirstCode = 101 because Peek('EmployeeCode',0, 'EmployeeDates') returns the first value of EmployeeCode in the table EmployeeDates. The contents of this structure appear to change greatly on other implementations, the glibc sources usually have some form of commenting but their structure for this is burried under a lot of code. Some believe that nobody in their right mind should make use of the Which includes the lovely comment before it: This is directly taken from my stdio.h, from MinGW32 5.1.4 typedef struct _iobuf ![]() The structure definition seems a little more illusive than its description. At the very least, you have to call peek on the first element in the list, so something like c0. The fopen function will return a pointer to a newly created FILE struct, assigning this new pointer to your unused one will cause them to point to the same thing.ĭoes it contain a stream to the file within and other data? c is a list, so youre trying to peek on a list. This is for example what fgets or fgetc will accept, in the form of function(FILE* fp) With a pointer to a struct, you can then pass it as a parameter to a function. What you are refering to is a typedef'd structure used by the standard io library to hold the appropriate data for use of fopen, and its family of functions. Is this a keyword or special data type for C to handle files with? ![]()
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