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Instance of SqRow is created by SqTypeRow. If SqTypeRow don't know type of columns, all data type in SqRow is C string.
SqArray
│
└─── SqRow
SqRow contain 2 arrays. One is column array, another is data array. In most cases, these two arrays will be the same length.
SqRow Structure Definition:
struct SqRow {
// data array
SqValue *data;
int length;
// column array
SqRowColumn *cols;
int cols_length;
};
There are hidden members in front of SqRow.data:
capacity is the number of elements actually allocated in the array. (excluding the header in front of the array)
Below is the code to access these hidden members:
// C functions
data_capacity = sq_row_capacity(row);
cols_capacity = sq_row_cols_capacity(row);
// C++ methods
data_capacity = row->capacity();
cols_capacity = row->colsCapacity();
SqRow use SqRowColumn array to store column name, column type, and column entry. SqRowColumn.type is always equal to SQ_TYPE_STR when SqTypeRow does not know the type of the column.
SqRowColumn Structure Definition:
struct SqRowColumn {
const char *name;
const SqType *type;
const SqEntry *entry;
};
SqRow use SqValue to store values. SqValue is a union type, the type of value is determined by the SqRowColumn.type at the same index.
SqValue Definition:
union SqValue {
bool bool_; // SQ_TYPE_BOOL
bool boolean; // SQ_TYPE_BOOL
int integer; // SQ_TYPE_INT
int int_; // SQ_TYPE_INT
unsigned int uinteger; // SQ_TYPE_UINT
unsigned int uint; // SQ_TYPE_UINT
int64_t int64; // SQ_TYPE_INT64
uint64_t uint64; // SQ_TYPE_UINT64
time_t rawtime; // SQ_TYPE_TIME
double fraction; // SQ_TYPE_DOUBLE
double double_; // SQ_TYPE_DOUBLE
const char *str; // SQ_TYPE_STR
const char *string; // SQ_TYPE_STR
const char *stream; // Text stream must be null-terminated string
void *pointer; // for user defined type
void *ptr; // for user defined type
};
For example, there is a row in customers table.
| id | name | state |
|---|---|---|
| 1 | Bob | NY |
If SqTypeRow does not know the type of the columns, arrays in SqRow should look like this:
// SqRow sqRow;
sqRow.cols[0].name = "id";
sqRow.cols[0].type = SQ_TYPE_STR;
sqRow.cols[0].entry = NULL;
sqRow.data[0].str = "1";
sqRow.cols[1].name = "name";
sqRow.cols[1].type = SQ_TYPE_STR;
sqRow.cols[1].entry = NULL;
sqRow.data[1].str = "Bob";
sqRow.cols[2].name = "state";
sqRow.cols[2].type = SQ_TYPE_STR;
sqRow.cols[2].entry = NULL;
sqRow.data[2].str = "NY";
// This row has 3 columns
sqRow.length = 3;
sqRow.cols_length = 3;
Otherwise the first column is this:
sqRow.cols[0].name = "id";
sqRow.cols[0].type = SQ_TYPE_INT;
sqRow.cols[0].entry = (const SqEntry*) pointerToSqColumn;
sqRow.data[0].integer = 1;
User must specify the pre-allocated length of the array when creating a SqRow.
use C language
SqRow *row;
int cols_capacity = 0; // pre-allocated length of column array
int data_capacity = 0; // pre-allocated length of data array
// create new SqRow
row = sq_row_new(cols_capacity, data_capacity);
// free SqRow
sq_row_free(row);
use C++ language
Sq::Row *row;
int colsCapacity = 0; // pre-allocated length of column array
int dataCapacity = 0; // pre-allocated length of data array
// create new Sq::Row
row = new Sq::Row(colsCapacity, dataCapacity);
// free Sq::Row
delete row;
SqRow can allocate memory for array of SqRowColumn and SqValue separately.
The C functions sq_row_alloc_column() and sq_row_alloc(), C++ methods allocColumn() and alloc() are used to allocate the column and its value.
use C language
int n_columns = 1;
int n_values = 1;
SqRowColumn *col = sq_row_alloc_column(row, n_columns);
SqValue *val = sq_row_alloc(row, n_values);
// set 'col' and 'val' here
col->name = strdup("id"); // It can be NULL if you don't need column name.
col->type = SQ_TYPE_INT; // SqRowColumn.type = SQ_TYPE_INT
col->entry = NULL; // It can be NULL.
val->integer = 1; // SqRowColumn.type = SQ_TYPE_INT
use C++ language
int nColumns = 1;
int nValues = 1;
Sq::RowColumn *col = row->allocColumn(nColumns);
Sq::Value *val = row->alloc(nValues);
// set 'col' and 'val' here
col->name = strdup("id"); // It can be NULL if you don't need column name.
col->type = SQ_TYPE_INT; // SqRowColumn.type = SQ_TYPE_INT
col->entry = NULL; // It can be NULL.
val->integer = 1; // SqRowColumn.type = SQ_TYPE_INT
Because all rows in the query result have the same column array, sharing the column array among these rows reduces memory usage. The C functions sq_row_share_cols(), C++ methods shareCols() can do this.
Note 1: If column array have been shared, user can not add/remove elements in it.
Note 2: When SqRow gets the shared column array, it frees its own column array.
use C language
SqRow *row = array->data[0]; // This 'array' has query result
// share SqRow::cols to other SqRow
for (int index = 1; index < array.length; index++)
sq_row_share_cols(row, array->data[index]);
use C++ STL
Sq::Row *row = vector->at(0); // The 'vector' has query result
// share SqRow::cols to other SqRow
for (cur = vector->begin()+1, end = vector->end(); cur != end; cur++)
row->shareCols(*cur);
The C functions sq_row_free_cols_name(), C++ methods freeColsName() can free all SqRowColumn.name in SqRow. This can save memory when you don't need them.
// C function
sq_row_free_cols_name(row);
// C++ method
row->freeColsName();
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