Andrey Karpov

Feb 04 2013

Tags:

#Cpp #64bit

How to correctly print a value of the types __int64, size_t, and ptrdiff_t

• 1. Using safe methods
• 2. Using a correct format string
• References

When developing an application, you may often face a trouble that variables of the types __int64, size_t, or ptrdiff_t are printed incorrectly. First of all we should mention the difference between these data types. The __int64 type, for instance, always has the size 64 bits both on the 32-bit and 64-bit platforms. The types size_t and ptrdiff_t are 32-bit on the 32-bit platform and 64-bit on the 64-bit platform. It is this point that causes troubles and confusion when printing values of these types.

There are two ways to eliminate the problem:

1. Using safe methods

For example, you can replace printf with cout, and sprintf with boost::format or std::stringstream.

2. Using a correct format string

a) For the __int64 type, regardless of the compiler (C++Builder, MSVC, or GCC):

printf("%lld", i);

b) For the types size_t and ptrdiff_t:

References

• Lessons on development of 64-bit C/C++ applications. Lesson 10. Pattern 2. Functions with variable number of arguments.
• Andrey Karpov. About size_t and ptrdiff_t.
• Knowledge Base. Difference between %p and %x.

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