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std::string &func(int vlu)
{
std::string str;
str = std::to_string(vlu) + "something";
return str;
}
the function above is unsafe clearly.
Following is another version.
std::string &func(int vlu)
{
return std::to_string(vlu) + "something";
}
I have some questions:
the compiler(gcc), in the second version, doesn't give me any warning. Is it safe?
I just think that compiler(or something?) will create a temporary variable to hold the return of expression std::to_string(vlu) + "something". So the second version is unsafe too. and I right?
210
Try this: std::string * sp; std::string func() { std::string s("bla"); sp = &s; return s; } int main() { std::string s = func(); if(sp == &s) std::cout << "YAY"; else std::cout << "BOO"; } -- On my compiler (VS) It prints YAY.
Use the std::string func() Notation to Return String From Function in C++ Return by the value is the preferred method for returning string objects from functions. Since the std::string class has the move constructor, returning even the long strings by value is efficient.
The std::string class manages the underlying storage for you, storing your strings in a contiguous manner. You can get access to this underlying buffer using the c_str() member function, which will return a pointer to null-terminated char array. This allows std::string to interoperate with C-string APIs.
string at() in C++ std::string::at can be used to extract characters by characters from a given string. Syntax 2: const char& string::at (size_type idx) const idx : index number Both forms return the character that has the index idx (the first character has index 0).
No, neither program is safe. In both cases the returned reference is dangling and the behaviour of using the reference will be undefined.
The second program is also ill-formed, because it attempts to bind an lvalue reference (that is returned) to an rvalue (the temporary). The second program might be considered "less unsafe", since a compiler might choose to not compile it.
To fix the function: Don't attempt to return a reference, when the purpose is to return a new object. Return an object instead.
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