My helper function is returning an empty string

Question

I'm writing some code for a game, and I'm attempting to write a helper function to return a string inside an object:

const char* getGhostName(GhostAI* ghostAI)
{
    if (ghostAI) {
        GhostInfo* ghostInfo = getGhostInfo(ghostAI);
        const auto ghostName = ghostInfo->fields.u0A6Du0A67u0A74u0A71u0A71u0A66u0A65u0A68u0A74u0A6Au0A6F.u0A65u0A66u0A6Eu0A67u0A69u0A74u0A69u0A65u0A74u0A6Fu0A67;
        const char* name = il2cppi_to_string(ghostName).c_str();
        return name;
    }
    return "UNKNOWN";
}

And here is the il2cppi_to_string functions:

std::string il2cppi_to_string(Il2CppString* str) {
    std::u16string u16(reinterpret_cast<const char16_t*>(str->chars));
    return std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t>{}.to_bytes(u16);
}

std::string il2cppi_to_string(app::String* str) {
    return il2cppi_to_string(reinterpret_cast<Il2CppString*>(str));
}

When I call getGhostName, I end up with an empty string. Now I did get a warning from ReSharper which says:

Object backing the pointer will be destroyed at the end of the full-expression.

This is appearing on the following line inside getGhostName when calling il2cppi_to_string:

const char* name = il2cppi_to_string(ghostName).c_str();

I'm not entirely sure what this means or how I can modify the code to fix it. I absolutely hate working with strings in C++.

Why not just keep using actual std::strings instead of trying to juggle char pointers? — Quentin
– Quentin, Commented Mar 20, 2022 at 20:09
You are calling c_str on a temporary std::string object that will be destroyed before your return statement. — jkb
– jkb, Commented Mar 20, 2022 at 20:09
"I absolutely hate working with strings in C++." -- I'd say you just need to read a tutorial on C++ strings. You hate it because you're trying to fight a system that you don't understand. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Mar 20, 2022 at 20:13
"I absolutely hate working with strings in C++." -- Yet you decided to use const char * instead of staying with the much-easier-to-use std::string. You sabotaged yourself by using const char *. — PaulMcKenzie
– PaulMcKenzie, Commented Mar 20, 2022 at 20:21
Does this answer your question? Why does calling std::string.c_str() on a function that returns a string not work? — JaMiT
– JaMiT, Commented Mar 20, 2022 at 20:23

Remy Lebeau · Accepted Answer · 2022-03-20 20:13:28Z

7

il2cppi_to_string() returns a temporary std::string, which will be destroyed at the end of the expression that calls il2cppi_to_string(). You are obtaining a const char* pointer to the data of that temporary std::string, which is what ReSharper is warning you about. Since the temporary std::string is destroyed before the return, that means getGhostName() is returning a dangling pointer to invalid memory.

To fix this, change getGhostName() to return a std::string instead of a const char*:

std::string getGhostName(GhostAI* ghostAI)
{
    if (ghostAI) {
        GhostInfo* ghostInfo = getGhostInfo(ghostAI);
        const auto ghostName = ghostInfo->fields.u0A6Du0A67u0A74u0A71u0A71u0A66u0A65u0A68u0A74u0A6Au0A6F.u0A65u0A66u0A6Eu0A67u0A69u0A74u0A69u0A65u0A74u0A6Fu0A67;
        return il2cppi_to_string(ghostName);
    }
    return "UNKNOWN";
}

answered Mar 20, 2022 at 20:13

Remy Lebeau

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