No type named 'function' in namespace std [closed]
Question
I wanted to pass lambdas around, so I defined a function like this:
double getInput(std::string inputDescription, std::function<bool(double)> isValid) { ... }
But gcc refused to compile it. I quickly learned I needed a compiler with C++11 support, so I downloaded clang 3.5 with MacPorts. I located clang++ and confirmed it was the right version (and I wasn't accidentally using the original clang 1.7):
$ /opt/local/bin/clang++ --version
clang version 3.5.0 (trunk 210448)
Target: x86_64-apple-darwin10.8.0
Thread model: posix
But even Clang 3.5 gives me:
tempConverter.cpp:14:52: error: no type named 'function' in namespace 'std'
double getInput(std::string inputDescription, std::function<bool(double)> isValid) {
~~~~~^
The full .cpp file:
#include <iostream>
#include <cmath>
#include <iomanip>
#include <functional>
#include <string>
static const double minTemp = -273.15;
static const double maxTemp = 500.0;
inline bool between(double x, double min, double max) {
return min <= x && x <= max;
}
double getInput(std::string inputDescription, std::function<bool(double)> isValid) {
double input;
std::cout << inputDescription << std::endl;
std::cin >> input;
while (!isValid(input)) {
std::cout << "Invalid input. Please reenter." << std::endl;
std::cin >> input;
}
return input;
/*double temp1, temp2;
std::cout << "Please enter consecutively the upper and lower limits, both between " << MIN_TEMP << " and " << MAX_TEMP << "." << std::endl;
std::cin >> temp1;
std::cin >> temp2;
while (!between(temp1, MAX_TEMP, MIN_TEMP) || !between(temp2, MAX_TEMP, MIN_TEMP)) {
std::cout << "At least one of the temperatures is out of bounds. Please reenter:" << std::endl;
std::cin >> temp1;
std::cin >> temp2;
}
upper = std::max(temp1, temp2);
lower = std::min(temp1, temp2);
std::cout << "Please enter a positive stepsize, smaller than the difference between the limits." << std::endl;
std::cin >> step;
while (step < 0 || step > upper - lower) {
std::cout << "The stepsize is out of bounds. Please reenter:" << std::endl;
std::cin >> step;
}*/
}
double toFahrenheit(double celsius) {
return celsius*(9.0/5.0) + 32;
}
void printTable(double start, double end, double step) {
std::cout << std::setw(10) << "Celsius" << "|" << std::setw(10) << "Fahrenheit" << std::endl;
std::cout << std:setw(10) << "=======" << "|" << std::setw(10) << "==========" << std::endl;
for (double i = start; i < end; i += step) {
std::cout << std::setw(10) << i << "|" << std::setw(10) << toFahrenheit(i) << std::endl;
}
}
int main() {
double start = getInput("Please enter the upper limit.", [](double x) { return between(x, minTemp, maxTemp); });
double end = getInput("Please enter the lower limit.", [&](double x) { return x < start && between(x, minTemp, maxTemp); });
double step = getInput("Please enter the stepsize.", [&](double x) { return x < end - start && x > 0; });
printTable(start, end, step);
}
Is compiled with:
/opt/local/bin/clang++ -std=c++11 tempConverter.cpp -o tempConverter
Solution
You forgot to:
#include <functional>
or you forgot the C++11 flag:
-std=c++11 -stdlib=libc++
OTHER TIPS
You need a C++11 library and #include <functional>
as well as a C++11 compiler.
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