Initializing a vector of string_view the wrong way?

Question

Bonjour,

Could please tell me why the first 3 lines do not work while the last 3 ones work?

See : https://gcc.godbolt.org/z/qozEsc

#include <vector>
#include <string_view>
#include <iostream>

int main(){

    const std::vector<std::string> W = {"aaa", "bbbb", "ccccc"};
    
    std::vector<std::string_view> Wbak1;
    for (std::string w : W) Wbak1.push_back(w.c_str());
    for(auto w:Wbak1) std::cout << w << '\n';

    std::vector<std::string_view> Wbak2;
    for (auto i = 0U; i < W.size(); ++i) Wbak2.push_back(W[i].c_str());
    for(auto w:Wbak2) std::cout << w << '\n';
}

Best regards, 40tude

Answer 1

In the 1st range-based for loop, w is a copy of the element of W. After each loop iteration, w is destroyed, leaving the w.c_str() pointer held by std::string_view dangling.

You should declare w as a reference. e.g.

for (const std::string& w : W) Wbak1.push_back(w.c_str());