Promotic

Object PmBuffer (Binary data memory)

Description:
The object represents binary values in data block. Data block (buffer) is a continuous area in the memory. For reading/writing of individual value it is necessary to know its position (offset) in the data block and also the data type (size).
General properties and methods:
AutoOffsetInternal automated position in the data block
SetSizeSetting the data block size
GetSizeDetects data block size
GetLastErrorReturns the flag of the last error
SetBufferWriting data block in the form of the PmBuffer object
GetBufferReading the data block in the form of the PmBuffer object
SetPtrWriting pointer (address) to another data block in the form of the PmBuffer object
GetPtrMock reading (skipping) of pointer to another data block
LoadFromFileReading values from binary file into the data block
SaveToFileWriting values from data block into a binary file
CalcCheckSumDetection of the data block check sum (hash)
Methods for writing and reading numeric value:
SetBitWriting a single bit
GetBitReading the value of one bit
SetInt8Writing integer 1 byte value
GetInt8Reading the integer 1 byte value
SetUint8Writing integer 1 byte unsigned value
GetUint8Reading integer 1 byte unsigned value
SetInt16Writing integer 2 byte value
GetInt16Reading the integer 2 byte value
SetUint16Writing integer 2 byte unsigned value
GetUint16Reading integer 2 byte unsigned value
SetInt32Writing integer 4 byte value
GetInt32Reading the integer 4 byte value
SetUint32Writing integer 4 byte unsigned value
GetUint32Reading integer 4 byte unsigned value
GetFloat32Reading the real 4 byte value
SetFloat32Writing real 4 byte value
GetFloat64Reading the real 8 byte value
SetFloat64Writing real 8 byte value
Methods for writing and reading String type value:
SetStringFixWriting the text string with fixed length
GetStringFixReading the text string with fixed length
SetStringVarWriting the text string with variable length (terminated by the NULL character)
GetStringVarReading the text string with variable length (terminated by the NULL character)
SetHexaStringWriting data block in the form of HexaString
GetHexaStringReading the data block in the form of HexaString
SetBase64StringWriting data block in the form of Base64String
GetBase64StringReading the data block in the form of Base64String
Note:
- The object can be created by the Pm.CreatePmBuffer method.
- This object is functional also in Web panels.

Comparison of objects used for data storage:
The following object types can be used for holding values (of any data type). Each of these objects has certain advantages and disadvantages and the choice depends on the desired usage.
PmArray: This object contains values that are accessible by index into the array - it is possible to read any value at any time in this object. Reading and writing values is very fast, but adding is slow.
This object is functional only for JavaScript language. For the VBScript language the array is represented by Array data type.
PmMap: This object contains values that are addressed by name (text identifier). Value names represent object properties. The advanatege is the "clarity" of usage in the script code. The disadvantage is the inability to access the values in cycle by index.
PmBuffer: This object contains binary values in data block. For reading/writing of individual value it is necessary to know its position (offset) in the data block and also the data type (size).
See also:
- An example that uses the PmBuffer object to create, edit and save into a file a table in the dbf format.
Example1:
JavaScriptSelect and copy to clipboard

var oBuf = Pm.CreatePmBuffer();
// Setting the whole content of the data block as HexaString and partial reading of its content into 3 variables of different types
var s1 = "40302010605070";   // The HexaString contains 7 bytes with values 0x40 0x30 0x20 0x10 0x60 0x50 0x70
oBuf.SetHexaString(-2, s1);   // Filling the data block with data from HexaString
oBuf.AutoOffset = 0;   // Setting the automatic position back to beginning
var i32 = oBuf.GetInt32(-4);   // Reading the value into the variable: 0x10203040
var i16 = oBuf.GetInt16(-4);   // Reading the value into the variable: 0x5060
var ui8 = oBuf.GetUint8(-4);   // Reading the value into the variable: 0x70
// Continuous creation of data block by writing 3 variables and then obtaining the whole content as HexaString
oBuf.SetSize(0);   // Setting the new size to 0 and deleting (resetting) of existing content of the data block
oBuf.SetInt32(-2, i32);   // Adds the value from variable to the end: 0x10203040
oBuf.SetInt16(-2, i16);   // Adds the value from variable to the end: 0x5060
oBuf.SetUint8(-2, ui8);   // Adds the value from variable to the end: 0x70
var s2 = oBuf.GetHexaString(0);   // Reading the data block as HexaString. The read value s2 is the same as the original input value s1
Example2:
Reading 4 bytes of the data block by bytes as HexaString or in decimal
JavaScriptSelect and copy to clipboard

var oBuf = Pm.CreatePmBuffer();
oBuf.SetSize(4);
oBuf.SetInt32(0, 1020304050, 0);

Pm.Debug("Hexastring=" + oBuf.GetHexaString());

oBuf.AutoOffset = 0;
var h0 = oBuf.GetHexaString(-4, 1);
var h1 = oBuf.GetHexaString(-4, 1);
var h2 = oBuf.GetHexaString(-4, 1);
var h3 = oBuf.GetHexaString(-4, 1);
Pm.Debug("Hexastring=" + h0 + ", " + h1 + ", " + h2 + ", " + h3);

oBuf.AutoOffset = 0;
var v0 = oBuf.GetUint8(-4);
var v1 = oBuf.GetUint8(-4);
var v2 = oBuf.GetUint8(-4);
var v3 = oBuf.GetUint8(-4);
Pm.Debug("GetUint8=" + v0 + ", " + v1 + ", " + v2 + ", " + v3);

History:
Pm9.00.05:
- LoadFromFile and SaveToFile new methods: These methods allow writing or reading into/from a binary file. These methods replace methods Pm.FileBinaryRead and Pm.FileBinaryWrite that are not functional in the JavaScript language and therefore considered obsolete.
- GetBit and SetBit new methods: Methods allowing bit access into a data block.
Pm9.00.04: Created
PROMOTIC 9.0.21 SCADA system documentation - MICROSYS, spol. s r.o.

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