c++ - 转换字符串 vector : skip elements based on the previous value

Question

我需要将字符串 vector 转换为小写，但我需要保留文件名的大小写。它们由前面的字符串标记“file”或“out”标识。

#include <iostream>
#include <algorithm>
#include <vector>
#include <iterator>

template <class T>
void print(const T& v) {
    std::copy(v.begin(), v.end(), 
            std::ostream_iterator<typename T::value_type>(std::cout, "\n"));
}

std::string lowercase(const std::string& s) 
{
    std::string result(s);
    std::transform(result.begin(), result.end(), result.begin(), ::tolower);
    return result;
}

int main() {

    std::vector<std::string> tokens {"Col1", "Col2", "File", "FileIn.dat", "Out", "FileOut.dat"};
    std::transform(tokens.begin(), tokens.end(), tokens.begin(), lowercase);

    // how to replace lowercase() with a lambda that will take the previous
    // element into account while converting an element into lowercase
    print(tokens);

    return 0;
}

在上面的代码中结果应该是

{"col1", "col2", "file", "FileIn.dat", "out", "FileOut.dat"};

保留“file”和“out”之后字符串的大小写。

有没有办法使用 std::transform 和 lambda 函数来做到这一点？

Answer 1

是的。您可以像这样使用捕获 lambda:

bool is_filename = false;
std::transform(tokens.begin(), tokens.end(), tokens.begin(),
    [&is_filename] (auto &s) {
        if (is_filename)
            is_filename = false;
        else  
        {
            s = lowercase (s);
            is_filename = s == "file" || s == "out";
        }
        return s;
    });

输出:

col1
col2
file
FileIn.dat
out
FileOut.dat

Live demo