C++ vector of strings segfault

Question

can anyone tell me why this segfaults?

vector<string> vec;
for (int i = 0; i < 1000000; /* 1 million */ i++) {
    vec.push_back("string"+i);
}

Compiled in g++ with -std=c++14

It doesn't. It applies weird pointer arithmetics. You're accessing addresses that are out of range, and you're not having rights to access. — πάντα ῥεῖ, Sep 24 '16 at 06:19
@iPherian C++ is not like those other languages you know. You should probably start [here](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). — molbdnilo, Sep 24 '16 at 06:20
`"string"` is not actually a `string` (meaning an instance of the `std::string` class), by the way; it's an *array of `const char*`*. — Kyle Strand, Sep 24 '16 at 06:27
@VioletGiraffe ...right, didn't mean to say it was an array of pointers. Oops. — Kyle Strand, Sep 24 '16 at 15:43

score 4 · Accepted Answer · answered Sep 24 '16 at 06:21

As panta-rei correctly pointed out, it looks like you're trying to contain a string of the form

"string" + string form of (i)

but you're actually doing pointer arithmetic which is illogical in this case (you're just passing a pointer incremented i from some location - who knows what's in that memory?).

In order to do what you want, you can use std::to_string, which will translate i to a proper C++ string. The addition of a C-style string with that, is OK.

Change your line to

vec.push_back("string"+to_string(i));

score 2 · Answer 2 · answered Sep 24 '16 at 06:20

2

vector<string> vec;
for (int i = 0; i < 1000000; i++) {
    vec.push_back("string" + to_string(i));
}

this is not PHP...

answered Sep 24 '16 at 06:20

Frederick Zhang

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C++ vector of strings segfault

2 Answers2