I want to do the following:
std::unique_ptr<char[]> buffer = new char[ /* ... */ ] { "/tmp/file-XXXXXX" };
Obviously, it doesn't work because I haven't specified the size of a new array. What is an appropriate way to achieve my goal without counting symbols in a string literal?
Usage of std::array is also welcome.
Update #1: even if I put the size of array, it won't work either.
Update #2: it's vital to have a non-const access to the array as a simple char* pointer.
Here's a solution based on std::array:
std::array<char, sizeof("/tmp/file-XXXXXX")> arr{ "/tmp/file-XXXXXX" };
You can reduce the boilerplate using a macro:
#define DECLARE_LITERAL_ARRAY(name, str) std::array<char, sizeof(str)> name{ str }
DECLARE_LITERAL_ARRAY(arr, "/tmp/file-XXXXXX");
The sizeof is evaluated at compile-time, so there is no runtime scanning of the literal string to find its length. The resulting array is null-terminated, which you probably want anyway.
Since you requested a dynamic array and not wanting to count the length, that rules out std::array<char,N>. What you're asking for is really just std::string - it's dynamic (if need be), and initializes just fine from a char* without counting the length. Internally, it stores the string in a flat array, so you can use it as such, via the c_str() call.
string since the array will go as non-const char* to mkstemp()
string object with a literal string, and then calling c_str in order to retrieve the char array would make this answer even better.
mkstemp() modifies its argument, you're right that we need non-const memory. Two options: const_cast<char*>(str.c_str()) ... which is awful, but it's your string and mkstemp() doesn't change the length, so it might be ok. Or you will need to count chars and use the std::array. Or you can do: char* buf = new char[strlen(template)]; copy(template.begin(),template.end(),buf.begin());
str.c_str() != &str[0], otherwise the original storage is guaranteed to be mutable and hence const can be legally cast away.I don't get why you're not using std::string; you can do str.empty() ? NULL : &str[0] to get a non-const pointer, so the constness of str.c_str() is not going to pose a problem.
However, note that this is not null-terminated.
string- which incidentally offers the right constructor too. Wellsizeof("/tmp/lala")will work for the size if it's a constant (that includes the\0too though so be careful).