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20.2 Types de données C API

MYSQL

This structure represents a handle to one database connection. It is used for almost all MySQL functions.

MYSQL_RES

This structure represents the result of a query that returns rows (SELECT, SHOW, DESCRIBE, EXPLAIN). The information returned from a query is called the result set in the remainder of this section.

MYSQL_ROW

This is a type-safe representation of one row of data. It is currently implemented as an array of counted byte strings. (You cannot treat these as null-terminated strings if field values may contain binary data, because such values may contain null bytes internally.) Rows are obtained by calling mysql_fetch_row().

MYSQL_FIELD

This structure contains information about a field, such as the field's name, type and size. Its members are described in more detail below. You may obtain the MYSQL_FIELD structures for each field by calling mysql_fetch_field() repeatedly. Field values are not part of this structure; they are contained in a MYSQL_ROW structure.

MYSQL_FIELD_OFFSET

This is a type-safe representation of an offset into a MySQL field list. (Used by mysql_field_seek().) Offsets are field numbers within a row, beginning at zero.

my_ulonglong

The type used for the number of rows and for mysql_affected_rows(), mysql_num_rows() and mysql_insert_id(). This type provides a range of 0 to 1.84e19. On some systems, attempting to print a value of type my_ulonglong will not work. To print such a value, convert it to unsigned long and use a %lu print format. Example:

printf (Number of rows: %lu\n", (unsigned long) mysql_num_rows(result));

The MYSQL_FIELD structure contains the members listed below:

char * name

The name of the field.

char * table

The name of the table containing this field, if it isn't a calculated field. For calculated fields, the table value is a NULL pointer.

char * def

The default value of this field (set only if you use mysql_list_fields()).

enum enum_field_types type

The type of the field. The type value may be one of the following:

Type value	Type meaning
FIELD_TYPE_TINY	TINYINT field
FIELD_TYPE_SHORT	SMALLINT field
FIELD_TYPE_LONG	INTEGER field
FIELD_TYPE_INT24	MEDIUMINT field
FIELD_TYPE_LONGLONG	BIGINT field
FIELD_TYPE_DECIMAL	DECIMAL or NUMERIC field
FIELD_TYPE_FLOAT	FLOAT field
FIELD_TYPE_DOUBLE	DOUBLE or REAL field
FIELD_TYPE_TIMESTAMP	TIMESTAMP field
FIELD_TYPE_DATE	DATE field
FIELD_TYPE_TIME	TIME field
FIELD_TYPE_DATETIME	DATETIME field
FIELD_TYPE_YEAR	YEAR field
FIELD_TYPE_STRING	String (CHAR or VARCHAR) field
FIELD_TYPE_BLOB	BLOB or TEXT field (use max_length to determine the maximum length)
FIELD_TYPE_SET	SET field
FIELD_TYPE_ENUM	ENUM field
FIELD_TYPE_NULL	NULL-type field
FIELD_TYPE_CHAR	Deprecated; use FIELD_TYPE_TINY instead

You can use the IS_NUM() macro to test whether or not a field has a numeric type. Pass the type value to IS_NUM() and it will evaluate to TRUE if the field is numeric:

if (IS_NUM(field->type))
    printf("Field is numeric\n");

unsigned int length

The width of the field.

unsigned int max_length

The maximum width of the field for the result set. If you used mysql_list_fields(), this contains the maximum length for the field.

unsigned int flags

Different bit-flags for the field. The flags value may have zero or more of the following bits set:

Flag value	Flag meaning
NOT_NULL_FLAG	Field can't be NULL
PRI_KEY_FLAG	Field is part of a primary key
UNIQUE_KEY_FLAG	Field is part of a unique key
MULTIPLE_KEY_FLAG	Field is part of a non-unique key.
UNSIGNED_FLAG	Field has the UNSIGNED attribute
ZEROFILL_FLAG	Field has the ZEROFILL attribute
BINARY_FLAG	Field has the BINARY attribute
AUTO_INCREMENT_FLAG	Field has the AUTO_INCREMENT attribute
ENUM_FLAG	Field is an ENUM (deprecated)
BLOB_FLAG	Field is a BLOB or TEXT (deprecated)
TIMESTAMP_FLAG	Field is a TIMESTAMP (deprecated)

Use of the BLOB_FLAG, ENUM_FLAG and TIMESTAMP_FLAG flags is deprecated because they indicate the type of a field rather than an attribute of its type. It is preferable to test field->type against FIELD_TYPE_BLOB, FIELD_TYPE_ENUM or FIELD_TYPE_TIMESTAMP instead. The example below illustrates a typical use of the flags value:

if (field->flags & NOT_NULL_FLAG)
    printf("Field can't be null\n");

You may use the following convenience macros to determine the boolean status of the flags value:

IS_NOT_NULL(flags)	True if this field is defined as NOT NULL
IS_PRI_KEY(flags)	True if this field is a primary key
IS_BLOB(flags)	True if this field is a BLOB or TEXT (deprecated; test field->type instead)

unsigned int decimals

The number of decimals for numeric fields.

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