I need to convert a bool to a text string. Does anyone know how to do that?
I tried to use (std::string)bool syntax but it didn't work.
CodePudding user response：
The C standard does not define any direct conversions between std::string and bool. However, operator<< and operator>> for I/O streams do have such conversions defined.
In this case, you can use a std::ostringstream to format a bool into a std::string, eg:
std::ostringstream oss;
oss << theBoolValue;
std::string s = oss.str();
By default, that will output "1" for true and "0" for false. If you want the output to actually say "true" or "false" instead, you can use the std::boolalpha I/O manipulator, eg:
oss << std::boolalpha << theBoolValue;
Alternatively, in C 20 and later, you can use std::format() (in earlier versions, you can use the {fmt} library), eg:
std::string s = std::format("{}", theBoolValue); // returns "true" or "false"
std::string s = std::format("{:L}", theBoolValue); // returns the locale-specific representation
std::string s = std::format("{:d}", theBoolValue); // returns "1" or "0"
// other supported numeric formats:
// {:b} and {:B} for binary, "0b..." lowercase and "0B..." uppercase
// {:o} for octet, "0..."
// {:x} and {:X} for hex, "0x..." lowercase and "0X..." uppercase
CodePudding user response：
This is what Sam Varshavchik suggested in comment, basically, that is it:)
bool b;
...
printf("b is %s\n"
, b ? "true" : "false"
);
CodePudding user response：
#include <string>
#include <iostream>
namespace vt {
static constexpr auto as_string(const bool x) -> std::string {
return (x) ? "true" : "false";
}
} // namespace vt
int main(int argc, char** argv) {
const auto x = argv[argc] != nullptr;
// NB: argv[argc] is always nullptr so it's false.
// Using a turnary to initialize a std::string
// (See: https://en.cppreference.com/w/cpp/language/operator_other)
const auto k0 = std::string(x ? "true" : "false");
std::cout << "k0 = std::string(x ? \"true\" : \"false\"):\t" << k0 << "\n";
// Using a function to achieve the same.
const auto k1 = vt::as_string(x);
std::cout << "k1 = vt::as_string(x):\t\t\t" << k1 << "\n";
// If you need a string but you're fine with "0"/"1" over "false"/"true"
const auto k2 = std::to_string(x); // x is implicitly converted to int
std::cout << "k2 = std::to_string(x):\t\t\t" << k2 << "\n";
// If you only intend to write to a std::ostream you don't need a string.
std::cout << "std::cout << std::boolalpha << x:\t"
<< std::boolalpha << x << std::endl;
}