Delphi 7 null

Suppose we are to change the value of the s2 string variable; Delphi copies the first string to a new memory location, since the change should affect only s2, not s1, and they are both pointing to the same memory location.

Wide strings are also dynamically allocated and managed, but they don't use reference counting or the copy-on-write semantics. Wide strings consist of bit Unicode characters. Unicode stores each character in the character set in 2 bytes instead of 1. Some national languages use ideographic characters, which require more than the characters supported by ANSI. With bit notation we can represent 65, different characters.

Indexing of multibyte strings is not reliable, since s[i] represents the ith byte not necessarily the i-th character in s. If you must use Wide characters, you should declare a string variable to be of the WideString type and your character variable of the WideChar type. If you want to examine a wide string one character at a time, be sure to test for multibite characters. Delphi doesn't support automatic type conversions betwwen Ansi and Wide string types.

A null or zero terminated string is an array of characters, indexed by an integer starting from zero. This means there is essentially no difference between a null-terminated string and an array[ NumberOfChars] of type Char, where the end of the string is marked by 0. Object Pascal lets us avoid messing arround with pointers to zero-based arrays when handling null-terminated strings by using the PChar type.

Think of a PChar as being a pointer to a null-terminated string or to the array that represents one. For more info on pointers, check: Pointers in Delphi. The following procedure lists all the drives and their types on a users computer. We can freely mix all four different kinds of strings, Delphi will give it's best to make sense of what we are trying to do.

A string constant of length 1, such as 'T', can denote a character value. The generic character type is Char, which is equivalent to AnsiChar.

WideChar values are bit characters ordered according to the Unicode character set. Actively scan device characteristics for identification.

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Develop and improve products. List of Partners vendors. Share Flipboard Email. By Zarko Gajic Zarko Gajic. Learn about our Editorial Process. Featured Video. Cite this Article Format. Gajic, Zarko. Ordinal and Enumerated Data Types for Delphi. Connect and share knowledge within a single location that is structured and easy to search.

Empty string is inserted into the database, but I need null there. What and where should I make change to accomplish this task. There is some difference in this delphi versions. Starting from delphi there is another memory manager that works more precise. In example in delphi 7 and lower you can assign NULL to string or integer value. And comparision NULL with 0 will return true.

In greater versions you can't do this. Null is not equal 0 or empty string. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 7 years, 10 months ago. Active 7 years, 10 months ago. Viewed 3k times. Delphi 7: Data is being inserted like this ds1. In Delphi XE4 , I am doing same like this: ds1.

Insert; ds1. FieldByName 'ID'. Post; Empty string is inserted into the database, but I need null there. Improve this question. Do not cast it AsString but use Value then. When you say, "I am doing same" that appears not to be true. Your D7 code does ds1. InsertRecord [, anyValue] ;. You don't do that in the XE4 code. Sorry for the creating the confusion.