问题
At my code, I do not use int or unsigned int. I only use size_t or ssize_t for portable. For example:
typedef size_t intc; // (instead of unsigned int)
typedef ssize_t uintc; // (instead of int)
Because strlen, string, vector... all use size_t, so I usually use size_t. And I only use ssize_t when it may be negative.
But I find that:
The unsigned integer types are ideal for uses that treat storage as a bit array. Using an unsigned instead of an int to gain one more bit to represent positive integers is almost never a good idea. Attempts to ensure that some values are positive by declaring variables unsigned will typically be defeated by the implicit conversion rules.
in the book The C++ Programming Language.
So I am puzzled. Am I wrong? Why does the STL not abide by the suggest on the book?
回答1:
ssize_t is used for functions whose return value could either be a valid size, or a negative value to indicate an error.
It is guaranteed to be able to store values at least in the range [-1, SSIZE_MAX] (SSIZE_MAX is system-dependent).
So you should use size_t whenever you mean to return a size in bytes, and ssize_t whenever you would return either a size in bytes or a (negative) error value.
See: http://pubs.opengroup.org/onlinepubs/007908775/xsh/systypes.h.html
回答2:
ssize_t is not included in the standard and isn't portable. size_t should be used when handling the size of objects (there's ptrdiff_t too, for pointer differences).
来源：https://stackoverflow.com/questions/15739490/should-use-size-t-or-ssize-t