[英]How to iterate over variadic function with std:string arguments?
void foo(std::string arg, ...) {
// do something with every argument
}
Lets say I want to be able to take every string argument and append an exclamation mark before printing it out on a new line.假设我希望能够获取每个字符串参数并在将其打印到新行之前附加一个感叹号。
The best way is to use parameters pack .最好的方法是使用参数 pack 。 For example:例如:
#include <iostream>
// Modify single string.
void foo(std::string& arg)
{
arg.append("!");
}
// Modify multiple strings. Here we use parameters pack by `...T`
template<typename ...T>
void foo(std::string& arg, T&... args)
{
foo(arg);
foo(args...);
}
int main()
{
// Lets make a test
std::string s1 = "qwe";
std::string s2 = "asd";
foo(s1, s2);
std::cout << s1 << std::endl << s2 << std::endl;
return 0;
}
This will print out:这将打印出:
qwe!
asd!
Use aparameter pack
with a fold expression
:使用带有fold expression
的parameter pack
:
#include <iostream>
#include <string>
// Modify multiple strings. Here we use parameters pack by `...T`
template<typename ...T>
void foo(T&... args)
{
(args.append("!"),...);
}
int main()
{
// Lets make a test
std::string s1 = "qwe";
std::string s2 = "asd";
foo(s1, s2);
std::cout << s1 << std::endl << s2 << std::endl;
return 0;
}
Here is an iterative solution.这是一个迭代解决方案。 There is a bit of noise in the function call, but no computation of the number of varargs is needed.函数调用中有一点噪音,但不需要计算可变参数的数量。
#include <iostream>
#include <string>
#include <initializer_list>
#include <functional> // reference_wrapper
void foo(std::initializer_list<std::reference_wrapper<std::string>> args) {
for (auto arg : args) {
arg.get().append("!");
}
}
int main() {
// Lets make a test
std::string s1 = "qwe";
std::string s2 = "asd";
foo({s1, s2});
std::cout << s1 << std::endl << s2 << std::endl;
return 0;
}
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