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For input, useMYSQL_BIND structures withmysql_stmt_bind_param() to bind parameter data values to buffers for use bymysql_stmt_execute().

For output, useMYSQL_BIND structures withmysql_stmt_bind_result() to bind buffers to result set columns, for use in fetching rows withmysql_stmt_fetch().

enum enum_field_types buffer_type

The type of the buffer. This member indicates the data type of the C language variable bound to a statement parameter or result set column. For input,buffer_type indicates the type of the variable containing the value to be sent to the server. For output, it indicates the type of the variable into which a value received from the server should be stored. For permissiblebuffer_type values, seeSection 6.2.1, “C API Prepared Statement Type Codes”.

void *buffer

A pointer to the buffer to be used for data transfer. This is the address of a C language variable.

For input,buffer is a pointer to the variable in which you store the data value for a statement parameter. When you callmysql_stmt_execute(), MySQL use the value stored in the variable in place of the corresponding parameter marker in the statement (specified with? in the statement string).

For output,buffer is a pointer to the variable in which to return a result set column value. When you callmysql_stmt_fetch(), MySQL stores a column value from the current row of the result set in this variable. You can access the value when the call returns.

To minimize the need for MySQL to perform type conversions between C language values on the client side and SQL values on the server side, use C variables that have types similar to those of the corresponding SQL values:

For guidelines about mapping between C types and SQL types and notes about type conversions, seeSection 6.2.1, “C API Prepared Statement Type Codes”, andSection 6.2.2, “C API Prepared Statement Type Conversions”.

unsigned long buffer_length

The actual size of*buffer in bytes. This indicates the maximum amount of data that can be stored in the buffer. For character and binary C data, thebuffer_length value specifies the length of*buffer when used withmysql_stmt_bind_param() to specify input values, or the maximum number of output data bytes that can be fetched into the buffer when used withmysql_stmt_bind_result().

unsigned long *length

A pointer to anunsigned long variable that indicates the actual number of bytes of data stored in*buffer.length is used for character or binary C data.

For input parameter data binding, set*length to indicate the actual length of the parameter value stored in*buffer. This is used bymysql_stmt_execute().

For output value binding, MySQL sets*length when you callmysql_stmt_fetch(). Themysql_stmt_fetch() return value determines how to interpret the length:

length is ignored for numeric and temporal data types because thebuffer_type value determines the length of the data value.

If you must determine the length of a returned value before fetching it, seeSection 6.4.11, “mysql_stmt_fetch()”, for some strategies.

my_bool *is_null

This member points to amy_bool variable that is true if a value isNULL, false if it is notNULL. For input, set*is_null to true to indicate that you are passing aNULL value as a statement parameter.

is_null is apointer to a boolean scalar, not a boolean scalar, to provide flexibility in how you specifyNULL values:

For output, when you fetch a row, MySQL sets the value pointed to byis_null to true or false according to whether the result set column value returned from the statement is or is notNULL.

my_bool is_unsigned

This member applies for C variables with data types that can beunsigned (char,short int,int,long long int). Setis_unsigned to true if the variable pointed to bybuffer isunsigned and false otherwise. For example, if you bind asigned char variable tobuffer, specify a type code ofMYSQL_TYPE_TINY and setis_unsigned to false. If you bind anunsigned char instead, the type code is the same butis_unsigned should be true. (Forchar, it is not defined whether it is signed or unsigned, so it is best to be explicit about signedness by usingsigned char orunsigned char.)

is_unsigned applies only to the C language variable on the client side. It indicates nothing about the signedness of the corresponding SQL value on the server side. For example, if you use anint variable to supply a value for aBIGINT UNSIGNED column,is_unsigned should be false becauseint is a signed type. If you use anunsigned int variable to supply a value for aBIGINT column,is_unsigned should be true becauseunsigned int is an unsigned type. MySQL performs the proper conversion between signed and unsigned values in both directions, although a warning occurs if truncation results.

my_bool *error

For output, set this member to point to amy_bool variable to have truncation information for the parameter stored there after a row fetching operation. When truncation reporting is enabled,mysql_stmt_fetch() returnsMYSQL_DATA_TRUNCATED and*error is true in theMYSQL_BIND structures for parameters in which truncation occurred. Truncation indicates loss of sign or significant digits, or that a string was too long to fit in a column. Truncation reporting is enabled by default, but can be controlled by callingmysql_options() with theMYSQL_REPORT_DATA_TRUNCATION option.