I/O Format Specifiers for Writing IEEE 488.2 Binary Blocks

IEEE Binary Block Data — %b and $B

An array argument formatted as an IEEE binary block has a format specifier of the following form:

%[array size] [$S] [b | h | l | I | z | Z] [b | B]

Modifier	Interpretation
Default Functionality	The data block is sent as an IEEE 488.2 definite-length binary block. The array size field specifies the number of elements (by default, bytes) in the block.
array size	Specifies the number of elements in the associated array argument. If the argument is a SAFEARRAY, then the array size may be omitted, in which case the number of elements sent is determined from the size of the SAFEARRAY itself. An asterisk (*) may be present in lieu of an integer array size modifier, in which case an extra int argument supplies the value.
$S	The argument is assumed to be a SAFEARRAY.
length modifier	If no length modifier is specified, then the argument is assumed to be an array (or SAFEARRAY if $S is used) of BYTE (8-bit) integer. b - argument is an array of BYTE (8-bit) integer. h - argument is an array of short (16-bit) integer. The array size indicates the number of 16-bit words, rather than the number of bytes. As per the 488.2 binary block standard, the data is sent with big-endian byte ordering. Byte-swapping is automatically performed on all elements in the array. l - argument is an array of long (32-bit) integer. The array size indicates the number of 32-bit words, rather than the number of bytes. As per the 488.2 binary block standard, the data is sent with big-endian byte ordering. Byte-swapping is automatically performed on all elements in the array. I - argument is an array of __int64 (64-bit) integer. The array size indicates the number of 64-bit words, rather than the number of bytes. As per the 488.2 binary block standard, the data is sent with big-endian byte ordering. Byte-swapping is automatically performed on all elements in the array. z - argument is an array of float (32-bit) floating-point numbers. The numbers are sent in IEEE 754 format. Z - argument is an array of double (64-bit) floating-point numbers. The numbers are sent in IEEE 754 format.
b	Data is sent as an IEEE 488.2 definite-length binary block.
B	Data is sent as an IEEE 488.2 indefinite-length binary block. A linefeed character (\n) is sent after the last byte of the block.

Example — Definite and indefinite-length blocks

HRESULT hr = S_OK;

short rgShortData[] = { 1.1, 1.2, 1.3, 1.4, 1.5 };

// IEEE definite-length block of 3 16-bit words
hr = io.Printf(_T("%3hb"), rgShortData);

// IEEE indefinite-length block of all 5 16-bit words
// Number of elements specified as a variable
int nCount = 5;
hr = io.Printf(_T("%*hB"), nCount, rgShortData);

CComSafeArray<double> saData;
saData.Add(1.1);
saData.Add(1.2);
saData.Add(1.3);

// Definite-length block of 3 doubles.  Argument is a SAFEARRAY.
// No field width supplied, so count is determined from the SAFEARRAY itself.
hr = io.Printf(_T("%$Zb"), saData.m_psa);

See also

• Printf