1. Off-warnings
2. Use of the functions with a variable number of arguments
3. Magic numbers
4. Storing of integers in double type
5. Bit shifting operations
6. Storing of pointer addresses
7. Memsize types in unions
8. Change of an array type
9. Virtual functions with arguments of memsize type
10. Serialization and data exchange
• The use of types of volatile size
• Ignoring of the byte order
11. Bit fields
12. Pointer address arithmetic
13. Arrays indexing
14. Mixed use of simple integer types and memsize types
15. Implicit type conversions while using functions
16. Overload functions
17. Data alignment
18. Exceptions
19. The use of outdated functions and predefined constants
20. Explicit type conversions

Introduction

We offer you to read the article devoted to the port of the program code of 32-bit applications on 64-bit systems. The article is written for programmers who use C++ but it may be also useful for all who face the port of applications on other platforms.

One should understand properly that the new class of errors which appears while writing 64-bit programs is not just some new incorrect constructions among thousands of others. These are inevitable difficulties which the developers of any developing program will face. This article will help you to be ready for these difficulties and will show the ways to overcome them. Besides advantages, any new technology (in programming and other spheres as well) carries some limitations and even problems of using this technology. The same situation can be found in the sphere of developing 64-bit software. We all know that 64-bit software is the next step of the information technologies development. But in reality, only few programmers have faced the nuances of this sphere and developing 64-bit programs in particular.

We won’t dwell on the advantages which the use of 64-bit architecture opens before programmers. There are a lot of publications devoted to this theme and the reader can find them easily.

The aim of this article is to observe thoroughly those problems which the developer of 64-bit programs can face. In the article you will learn about:

• typical errors of programming which occur on 64-bit systems;
• the reasons for appearing of these errors and the corresponding examples;
• methods of correcting the listed errors;
• the review of methods and means of searching errors in 64-bit programs.

• to learn the differences between 32-bit and 64-bit systems;
• to avoid errors while writing the code for 64-bit systems;
• to speed up the process of migration of a 32-bit application on the 64-bit architecture with the help of the great reducing of the time of debugging and testing;
• to forecast the time of porting the code on the 64-bit system more accurately and seriously.

To make the following text easier for understanding let’s remember some types first which we can face. (see table N1).

Type name	Type size (32-bit system)	Type size (64-bit system)	Description
ptrdiff_t	32	64	Signed integer type which appears after the subtraction of two pointers. It is used to keep sizes. Sometimes it is used as the result of function returning the size or -1 if an error occurs.
size_t	32	64	Unsigned integer type. The result of sizeof() operator. Is used to keep size or count of objects.
intptr_t, uintptr_t, SIZE_T, SSIZE_T, INT_PTR, DWORD_PTR, etc	32	64	Integer types capable to keep the pointer value.
time_t	32	64	Time in seconds.

_{Table N1. Description of some integer types.}

We’ll use term "memsize" type in the text. By this we’ll understand any simple integer type which is capable to keep a pointer and changes its size according to the change of the platform dimension form 32-bit to 64-bit. The examples memsize types: size_t, ptrdiff_t, all pointers, intptr_t, INT_PTR, DWORD_PTR.

We should say some words about the data models which determine the correspondence of the sizes of fundamental types for different systems. Table N2 contains data models which can interest us.

	ILP32	LP64	LLP64	ILP64
char	8	8	8	8
short	16	16	16	16
int	32	32	32	64
long	32	64	32	64
long long	64	64	64	64
size_t	32	64	64	64
pointer	32	64	64	64

_{Table N2. 32-bit and 64-bit data models.}

On default in this article we’ll consider that the program port will be fulfilled from the system with the data model ILP32 on systems with data model LP64 or LLP64.

And finally, 64-bit model in Linux (LP64) differs from that in Windows (LLP64) only in the size of long type. So long as it is their only difference, to summarize the account we’ll avoid using long, unsigned long types, and will use ptrdiff_t, size_t types.

Let’s start observing the type errors which occur while porting programs on the 64-bit architecture

Issues 1-4