What is the easiest way of getting a char array from a vector?
The way I am doing is getting a string initialized using vector begin and end iterators, and then getting .c_str() from this string. Are there other efficient methods?
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2 Answers
This was discussed in Scott Meyers' Effective STL, that you can do &vec[0] to get the address of the first element of an std::vector, and since the standard constrains vectors to having contiguous memory, you can do stuff like this.
// some function
void doSomething(char *cptr, int n)
{
}
// in your code
std::vector<char> chars;
if (!chars.empty())
{
doSomething(&chars[0], chars.size());
}
edit: From the comments (thanks casablanca)
- be wary about holding pointers to this data, as the pointer can be invalidated if the vector is modified.
1 Comment
casablanca
+1 but beware that the pointer may become invalid if the vector is modified later.
std::vector<char> chars;
char* char_arr = chars.data(); // &chars[0]
4 Comments
casablanca
data() isn't part of the standard STL specification.
ronag
It is part of the new C++0x STL (implemented both in MVSC and GCC), and should be used over &chars[0] if your compiler supports it.
Spille
@ronag: Why should it be preferred? Just because of readability or do other reasons exist?
x4444
@casablanca cplusplus.com/reference/vector/vector/data and en.cppreference.com/w/cpp/container/vector/data (since C++11)