How std::thread object copies argument? - c++11

Question

question updated !
I got a std::string object, and std::thread supposed to copy it into it's internal storage, why the code below still doesn't work?(FIXED)
If I detach t(f, 5, std::string(buf)), there are no output at all ! (FIXED)
#include <thread>
#include <iostream>
#include <unistd.h>
using namespace std;
void f(int i, const std::string &str) {
printf("i = %d, str = %s\n", i, str.c_str());
}
void oops(int ival) {
char *buf = new char[32]{0};
snprintf(buf, 32, "%i", ival);
// maybe danling pointer, if it's a danling pointer, the content of buf is undefined
// in this program it happens to be 1999.
std::thread t(f, 3, buf);
t.detach();
delete [] buf;
}
void not_oops(int ival) {
char *buf = new char[32]{0};
snprintf(buf, 32, "%i", ival);
std::thread t(f, 5, std::string(buf));
t.detach();
delete [] buf;
}
int main() {
oops(1992); // This is buggy
not_oops(1999);
}
expected output:
i = 3, str = 1992
i = 5, str = 1999
actual output:
i = 3, str = 1999
i = 5, str = 1999

Answer 1

Your program finishes before it is complete, your function exits scope before thread is complete, killing it.
void oops(int ival) {
char *buf = new char[32]{0};
snprintf(buf, 32, "%i", ival);
std::thread t(f, 3, buf); // maybe danling pointer
t.detach(); // no more waiting for it
delete [] buf; // thread is not started yet (probably)
} // thread is destroyed , and std::string dies.
Only way to make it work without vast changes to code, is to allow threads to be managed outside. Also you have to ensure that a new std::string is created, or thread appears to use same storage for both.
void f(int i, const std::string &str) {
printf("i = %d, str = %s\n", i, str.c_str());
}
std::thread *t;
void oops(int ival) {
char *buf = new char[32]{0};
snprintf(buf, 32, "%i", ival);
t = new std::thread(f, 3, std::string(buf)); // maybe danling pointer
//t.detach();
delete [] buf;
}
void not_oops(int ival) {
char *buf = new char[32]{0};
snprintf(buf, 32, "%i", ival);
std::thread t(f, 5, std::string(buf)); // FIXME: why it won't work ?
t.join();
delete [] buf;
}
int main() {
oops(1992); // This is buggy
not_oops(1999);
t->join();
delete t;
}