Argthtjtr

I run my code on an online judgement. I log the string, key. Below is my code:

fprintf(stderr, "key=%s, and key.size()=%dn", key.c_str(), key.size());

But the result is this:

key=^A, and key.size()=8

I want to what is the ^A represent in ascii. ^A's size is 2 rather than 8, but it shows that it is 8. I view the result by vim, and the log_file is encoded by UTF-8. Why?

Your viewer is electing to show you the bytes interpreted using a character encoding of its choosing and electing to show the resulting characters in caret notation.

Other viewers could make different choices on both counts or allow you to indicate what you want. For example, control picture characters (␁) instead of caret notation.

For a std:string c_str() is terminated by an additional x00 byte following the actual value. You often use c_str() with functions that expect a string to be x00 terminated. This applies to fprintf. In such cases, what's read ends just before the first x00 seen.

You have several x00 bytes in your string, which, of course, contributes to size() but fprintf will stop right at the first one (and not count it).

I have solve it by myself. If you write a std::string "x01x00x00x00x00end" to a file and open it with vim later, you will get '^A'.

This is my test code:

string sss("x01x00x00x00x00end");

ofstream of("of.txt");

for (int i=0; i<sss.size(); i++) {

    of.put(sss[i]);

}



of.close();

After I open the file "of.txt", I saw "^A";