Is there a way to get ascii value of a string representing a special character?

Question

I'm working on a compiler and I simply want to be able to read the literal '\n' as it's ascii value (10) in my language.

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But there are actually more escape sequence like \n and I don't want to attempt to account for all of them by myself when C++ already is fully capable of that.

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I basically need a way to take the array/string:

const char* s1 = {'\\'/* a simple slash */, 'n', '\0'}; // "\\n"
std::string s2 = "\\x002b"; // {'\\', 'x', '0', '0', '2', 'b', '\0'}

and treat it as the C/C++ compiler would have.

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I'd like a std functions to do it or if at runtime I could interact with the C++ compiler and let it do the job, something like this:

char c1 = exec("'%s'", s1); // would return '\n' as one character (ascii 10)
char c2 = std::parse_char_literal(s2); // would return '+' (ascii 43)

Thanks.