Function returning auto with auto parameter munmap_chunk(): invalid pointer

问题

I'm testing out new feature for GCC 4.9 (auto in parameter) and getting some weird bug.

#include <iostream>
#include <vector>

auto foo(auto v)
{
    for (auto&& i : v)
        std::cout << i;
}

int main()
{
    foo(std::vector<int>{1, 2, 3});
}

This is giving me the following error:

*** glibc detected *** ./a.out: munmap_chunk(): invalid pointer: 0x00007f87f58c6dc0 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x7e846)[0x7f87f4e4c846]
./a.out[0x400803]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xed)[0x7f87f4def76d]
./a.out[0x400881]

Also, if I do return 0 I get:

main.cpp: In instantiation of 'auto foo(auto:1) [with auto:1 = std::vector<int>]':
main.cpp:13:34:   required from here
main.cpp:8:12: error: could not convert '0' from 'int' to 'std::vector<int>'
     return 0;

Seems strange that both auto are deduced to be the same. What can I do to fix?

Note that the following works fine:

auto foo(auto v)
{
    return 'a';
}

int main()
{
    char c = foo(42);
}

My tests seem to indicate that pointers cause return type and v to be deduced to same. For example int* and make_unique<int>(42). However, vector is the one to give error.

回答1:

I dont think parameter types can be deduced that way – sp2danny

I belive that using auto like this invokes old auto meaning
(AFAIK, in this case auto=int, and int can't be converted to std::vector).

At the moment it works in lambdas

[](const auto& v)->void{for(auto&&i:v) std::cout<<i;}

But I think the best solution in this case is to write a template

template<typename T>
void foo(const T& t){
    for (auto&& i : t)
        std::cout << i;
}

来源：https://stackoverflow.com/questions/26571592/function-returning-auto-with-auto-parameter-munmap-chunk-invalid-pointer

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