Suppose I need to call a function foo
that takes a const std::string
reference from a great number of places in my code:
int foo(const
You may use something like to create your static std::string
"in place":
#include
#include
// Sequence of char
template struct char_sequence
{
template using push_back = char_sequence;
};
// Remove all chars from char_sequence from '\0'
template struct strip_sequence;
template
struct strip_sequence, Cs...>
{
using type = char_sequence;
};
template
struct strip_sequence, Cs2...>
{
using type = char_sequence;
};
template
struct strip_sequence, Cs2...>
{
using type = typename strip_sequence, Cs2..., C>::type;
};
// struct to create a std::string
template struct static_string;
template
struct static_string>
{
static const std::string str;
};
template
const
std::string static_string>::str = {Cs...};
// helper to get the i_th character (`\0` for out of bound)
template
constexpr char at(const char (&a)[N]) { return I < N ? a[I] : '\0'; }
// helper to check if the c-string will not be truncated
template
constexpr bool check_size(const char (&)[N])
{
static_assert(N <= max_size, "string too long");
return N <= max_size;
}
// Helper macros to build char_sequence from c-string
#define PUSH_BACK_8(S, I) \
::push_back(S)>::push_back(S)> \
::push_back(S)>::push_back(S)> \
::push_back(S)>::push_back(S)> \
::push_back(S)>::push_back(S)>
#define PUSH_BACK_32(S, I) \
PUSH_BACK_8(S, (I) + 0) PUSH_BACK_8(S, (I) + 8) \
PUSH_BACK_8(S, (I) + 16) PUSH_BACK_8(S, (I) + 24)
#define PUSH_BACK_128(S, I) \
PUSH_BACK_32(S, (I) + 0) PUSH_BACK_32(S, (I) + 32) \
PUSH_BACK_32(S, (I) + 64) PUSH_BACK_32(S, (I) + 96)
// Macro to create char_sequence from c-string (limited to 128 chars) without leading '\0'
#define MAKE_CHAR_SEQUENCE(S) \
strip_sequence \
PUSH_BACK_128(S, 0) \
::push_back(S) ? '\0' : '\0'> \
>::type
// Macro to return an static std::string
#define STATIC_STRING(S) static_string::str
Live example