[meta.trans.sign]

The templates specified in Table 59 convert an integer type to its corresponding signed or unsigned type.

Table 59 — Sign modifications [tab:meta.trans.sign]


template<class T> struct make_signed;	If T is a (possibly cv-qualified) signed integer type ([basic.fundamental]) then the member typedef type denotes T; otherwise, if T is a (possibly cv-qualified) unsigned integer type then type denotes the corresponding signed integer type, with the same cv-qualifiers as T; otherwise, type denotes the signed integer type with smallest rank ([conv.rank]) for which sizeof(T) == sizeof(type), with the same cv-qualifiers as T. Mandates: T is an integral or enumeration type other than cv bool.
template<class T> struct make_unsigned;	If T is a (possibly cv-qualified) unsigned integer type ([basic.fundamental]) then the member typedef type denotes T; otherwise, if T is a (possibly cv-qualified) signed integer type then type denotes the corresponding unsigned integer type, with the same cv-qualifiers as T; otherwise, type denotes the unsigned integer type with smallest rank ([conv.rank]) for which sizeof(T) == sizeof(type), with the same cv-qualifiers as T. Mandates: T is an integral or enumeration type other than cv bool.