一：功能
iota 是给定一个初始元素，然后依次对序列中每个元素进行递增++操作，详见代码一；
atoi 是将字符串转换成整数；atol, atoll 将字符串转换成长整型数 long，long long。
二：用法
#include <iostream>
#include <vector>
#include <numeric>
int main() {
std::vector<int> data(9, 0);
for (auto v : data)
std::cout << v << " ";
std::cout << "\n";
//对序列中元素进行累加， -4是初始值
std::iota(data.begin(), data.end(), -4);
for (auto v : data)
std::cout << v << " ";
std::cout << "\n";
//4 -3 -2 -1 0 1 2 3 4
}
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
printf("%i\n", atoi(" -123junk"));
printf("%i\n", atoi(" +321dust"));
printf("%i\n", atoi("0"));
printf("%i\n", atoi("0042")); // treated as a decimal number with leading zeros
printf("%i\n", atoi("0x2A")); // only leading zero is converted discarding "x2A"
printf("%i\n", atoi("junk")); // no conversion can be performed
printf("%i\n", atoi("2147483648")); // UB: out of range of int
}
