问题
For example, I use printf function in C++ for 8-bit CPU (AVR). Is the following code safe:
uint8_t a = 5;
printf(\"%d\", a);
Here %d expects int (16-bit in my case, and at least 16-bit in any case), but I pass 8-bit integer.
Does C/C++ standards guarantee that any type with rank lesser than int promoted to int?
The same question for float a and %f that expects double, and other analogous types.
回答1:
Look in the draft n1256 (C99 with Technical corrigenda TC1, TC2, and TC3 included) for 6.5.2.2 Function calls:
For functions without prototype, or parameters corresponding to the ellipsis ..., the default argument promotions are performed.
Those are: Default integer promotions and promotion of float to double.
Default integer promotions: Every integer type of rank less than int is promoted to int or unsigned int.
来源：https://stackoverflow.com/questions/22844360/what-default-promotions-of-types-are-there-in-the-variadic-arguments-list