C/C ++ 64-bit integer

From http://www.byvoid.com/blog/c-int64/

C/C ++ 64-bit integer

In C/C ++, 64 is an undefined standard data type. In today's mainstream compilers, the support for 64-type integers is also different in different forms. Generally, 64-bit integer types are long and _ int64 (VC also supports _ int64), while printf ("% LLD ", a), printf ("% i64d", A), and cout <.

This article discusses five common C/C ++ compilers that support 64-bit integers. These five compilers are GCC (mingw32), g ++ (mingw32 ), GCC (Linux i386), g ++ (Linux i386), Microsoft Visual C ++ 6.0. Unfortunately,There is no combination of definition and output methods, and these five compilers are compatible at the same time.. To thoroughly understand the 64-bit integer types of different compilers, I wrote a program to evaluate them. The results are shown in the following table.

Variable definition	Output Mode	GCC (mingw32)	G ++ (mingw32)	GCC (Linux i386)	G ++ (Linux i386)	Microsoftvisual C ++ 6.0
Long long	"% LLD"	Error	Error	Correct	Correct	Unable to compile
Long long	"% I64d"	Correct	Correct	Error	Error	Unable to compile
Int64	"LLD"	Error	Error	Unable to compile	Unable to compile	Error
Int64	"% I64d"	Correct	Correct	Unable to compile	Unable to compile	Correct
Long long	Cout	Non-C ++	Correct	Non-C ++	Correct	Unable to compile
_ Int64	Cout	Non-C ++	Correct	Non-C ++	Unable to compile	Unable to compile
Long long	Printint64 ()	Correct	Correct	Correct	Correct	Unable to compile

In the above table, correct indicates that the compilation passes and the operation is completely correct. Error indicates that the compilation passes but the running result is incorrect. Failure to compile means that the compiler cannot complete the compilation at all. Observe the table above and we can find the following points:

1. Long long can be defined in gcc/g ++ without platform restrictions, but not in vc6.0.
2. _ Int64 is a 64-bit long integer definition method of the Win32 platform compiler. It cannot be used in Linux.
3. "% LLD" is used for the Linux i386 platform compiler, and "% i64d" is used for the Win32 platform compiler.
4. Cout can only be used for C ++ compilation. In vc6.0, cout does not support 64-bit long integers.

Printint64 () in the output method of the last row in the table is a function written by myself. It can be seen that its compatibility is better than all other output methods. It is a piece of code like this:

void printint64(long long a){    if (a<=100000000)        printf("%d\n",a);    else    {        printf("%d",a/100000000);        printf("%08d\n",a%100000000);    }}

The essence of this writing method is to split the large 64-bit integer into two 32-bit integer types, and then output them in sequence. The low part must be supplemented with 0. What is the effect of seemingly stupid writing? I compared it with the cout output mode because it and cout both support cross-platform C ++. First, the running results of printint64 () and cout (do not clear the buffer) are identical and no error occurs. In my experiment, I used both to output 1000000 random numbers. The actual result is that printint64 () ran the program within 1.5s, and cout took 2 s. Cout is a little slower, so try to avoid using it when outputting a large amount of data.