uint8_t、uint16_t、...的格式说明符？

Question

If I have an integer variable I can use sscanf as shown below by using the format specifier %d.

sscanf (line, "Value of integer: %d\n", &my_integer);

Where can I find format specifiers for uint8_t , uint16_t , uint32_t and uint64_t ?

uint64_t has probably %lu.

Answer 1

They are declared in <inttypes.h> as macros: SCNd8, SCNd16, SCNd32 and SCNd64. Example (for int32_t):

sscanf (line, "Value of integer: %" SCNd32 "\n", &my_integer);

Their format is PRI (for printf)/SCN (for scan) then o, u, x, X d, i for the corresponding specifier then nothing, LEAST, FAST, MAX then the size (obviously there is no size for MAX). Some other examples: PRIo8, PRIuMAX, SCNoFAST16.

Edit: BTW a related question asked why that method was used. You may find the answers interesting.

Answer 2

As others said, include <stdint.h> header that defines the format macros. In C++, however, define __STDC_FORMAT_MACROS prior to including it. From stdint.h:

/* The ISO C99 standard specifies that these macros must only be
   defined if explicitly requested.  */
#if !defined __cplusplus || defined __STDC_FORMAT_MACROS

Answer 3

According to 7.19.6 Formatted input/output functions of ISO/IEC 9899:TC2 , there are no such format specifiers (so I doubt there any for C++2003). Even though there are some #define-macros available in C99's inttypes.h , cinttypes and inttypes.h are not part of the current standard. Of course, fixed-size integer types are non-standard as well.

Anyways, I seriously recommemend using streams instead:

<any_type> x;
f >> x;

and be done. Eg:

std::stringstream ss;
uint32_t u;
std::cin >> u;

This has the advantage that one time in the future, changing the type of the variable does not cause a cascade of subtle bugs and undefined behaviour.

Answer 4

The right format to read a uint64_t (typedef unsigned long long int) is, with scanf and not sscanf , "%" SCNu64 and for print is also SCNu64 Example. in your code you read for example my_integer variable, then you do scanf ("Value of integer:%" SCNu64, & my_integer); and to write the same but with printf.

Answer 5

You can check types in <cstdint> for C++ or in <types.h> for C. Then you can specify format which is currently compiled on your machine. If variable is unsigned then you need to use %u , if variable is signed , then use %d . For variables size lower than 32 bytes you don't have to specify long prefix.

In my configuration I have 64 bit program, so my uint64_t is compiled as unsigned long long int , so it means to use %llu . If your program will be compiled in 32 bit you can use %lu because uint64_t will be compiled as unsigned long int

But who is using x86 still? :), so generally:

uint8_t, uint16_t, uint32_t - %u
uint64_t - %llu
int8_t, int16_t, int32_t - %d
int64_t -%lld

Answer 6

In C, the header is <inttypes.h> , and formats such as SCNX8, SCNd16.

The same header probably works for C++ too.

Answer 7

Refer to this for sscanf usage.

These datatypes are defined in stdint.h. Refer here for stdint.h

Shash