String Type
The string type is used for storing text strings. A text string is a sequence of characters in the Unicode format with the final zero at the end of it. A string constant can be assigned to a string variable. A string constant is a sequence of Unicode characters enclosed in double quotes: "This is a string constant".
If you need to include a double quote (") into a string, the backslash character (\) must be put before it. Any special character constants can be written in a string, if the backslash character (\) is typed before them.
Examples:
string svar="This is a character string";
string svar2=StringSubstr(svar,0,4);
Print("Copyright symbol\t\x00A9");
FileWrite(handle,"This string contains a new line symbols \n");
string MT4path="C:\\Program Files\\MetaTrader 4"; |
To make the source code readable, long constant strings can be split into parts without addition operation. During compilation, these parts will be combined into one long string:
//--- Declare a long constant string
string HTML_head="<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\""
" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">\n"
"<html xmlns=\"http://www.w3.org/1999/xhtml\">\n"
"<head>\n"
"<meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\" />\n"
"<title>Trade Operations Report</title>\n"
"</head>";
//--- Output the constant string into log
Print(HTML_head);
} |
Internal representation of the string type is a structure of 12 bytes long:
#pragma pack(push,1)
struct MqlString
{
int size; // 32-bit integer, contains size of the buffer, allocated for the string.
LPWSTR buffer; // 32-bit address of the buffer, containing the string.
int reserved; // 32-bit integer, reserved.
};
#pragma pack(pop,1) |
See also
Conversion Functions, String Functions, FileOpen(), FileReadString(), FileWriteString()
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