How can i access the char array inside of an std::string?

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I was given a task to write a file system in Linux that simulates a storage device as a file.

One of the functions I was given needs to read data inside a "file". To do so I have a function that's supposed to return an std::string.

How can I read the data out of the file with the following function directly into an std::string?

void read(int addr, int size, char *ans)

Is there a way to pass the char array inside of an std::string as a parameter to this function? All of the methods and member functions I have encountered so far only return const char* which doesn't work in this case.

Thanks!

stdstring arrays c++
2 Answers

The conventional way of doing this is to pass a pointer to the string’s first character. This is guaranteed to work because the standard guarantees that the characters inside a std::basic_string are stored contiguously ([basic.string]/2).

Thus,

read(addr, str.size(), & str[0]);

works, but only if you have previously resized the string to a non-zero size. Additionally, your read function doesn’t tell you how many characters were read. There needs to be some functionality in your IO API to tell you this.

user_19680

Actually, it is bad idea to do so, as then std::string class doesn't know, how many characters were inserted. It is much better to create local buffer std::array<char, 256> buf, pass it to function, and then put it into std::string using std::string(buf.data, buf.size()).

user_131397610
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