How to print raw std::string/c-style character string in c++

Question

string str = "hello/nblabla/nblabla";
cout << str << endl;

how do I make output of this program be: hello/nblabla/nblabla if I can't use // and generally don't know what string contains. I would like to do the same with c-style char strings as well, and I need to print /0 if it appears in the middle of a c-style string.

I have code something like:

fin >> str;
stuff_to_do(str);
cout << str << endl;

where fin is a std::ifstream to a file containing data like: 123/nb/t/0/1/"... I can't reformat this file.

First of all, and sorry to be a nitpicker, but it's \ , not /. (Big difference.) — Steve Summit
– Steve Summit, Commented Jul 23, 2018 at 15:57
Make a lookup table and use it to convert special characters into escape sequences before printing. — Quentin
– Quentin, Commented Jul 23, 2018 at 15:59
You'll need to write a function that moves along the string a character at a time, printing it a character at a time. If the character you're looking at is '\n', print it as the two characters '\' and 'n'. If it's any other special character, print it using some other special character sequence. Otherwise (if it's a regular character), print it as itself. — Steve Summit
– Steve Summit, Commented Jul 23, 2018 at 16:01
Does your input file contain the two characters '\' and 'n', or the single character '\n'? (Again, big difference.) — Steve Summit
– Steve Summit, Commented Jul 23, 2018 at 16:04

SynAck · Accepted Answer · 2018-07-23 20:34:46Z

2

Use raw string literal.

string str = R"(hello\nblabla\nblabla)";
cout << str << endl;

output: hello\nblabla\nblabla
this works for null-terminated strings too!

edited Jul 23, 2018 at 20:34

answered Jul 23, 2018 at 20:21

SynAck

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Comments

Wyck · Accepted Answer · 2018-07-23 20:19:27Z

I think you need an escaping function that takes arbitrary text and escapes it so that it uses the syntax of a C++ string literal (minus the quotes). Maybe look around the web to see if there's a library already doing this.

There are some conventions to apply because there are multiple ways to escape a character.

I don't love this code, but here's an implementation I quickly put together to illustrate:

#include <string>
#include <iostream>
#include <sstream>
#include <iomanip>

const char* staticMap(char c) {
    switch (c) {
        case '\a': return "\\a";
        case '\b': return "\\b";
        case '\t': return "\\t";
        case '\n': return "\\n";
        case '\v': return "\\v";
        case '\f': return "\\f";
        case '\r': return "\\r";

        case '\"': return "\\\"";
        case '\'': return "\\\'";
        case '\?': return "\\\?";
        case '\\': return "\\\\";
    }
    return nullptr;
}

std::string escape_cpp(const std::string& input) {
    std::stringstream ss;
    for (char c : input) {
        const char* str = staticMap(c);
        if (str) { 
            ss << str;
        } else if (!isprint(static_cast<unsigned char>(c))) {
            ss << "\\u" << std::hex << std::setfill('0') << std::setw(4) << (static_cast<unsigned int>(static_cast<unsigned char>(c)));
        } else {
            ss << c;
        }
    }
    return ss.str();
}

int main() {

    std::string foo("bu\u00ffffalo\n\"\tw\u0000rld\"", 17);
    // Will be printed as written (by convention).
    std::cout << escape_cpp(foo) << std::endl;
}

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