如何在C ++中的字符串中显式打印“ \\ n”

Question

hi i have a unknown string in c++ containing "\\n" "\\t" etc. say;

string unknown1=read_from_file();

if unknown1="\\n\\t\\n\\t\\n\\n\\n\\n\\n" now I want to print

"\n\t\n\t\n\n\n\n\n"

to the screen explcitly other than a bunch of empty spaces.... how should I do that? remember that I don't know what is in unknown1...

to emphasize, I know that we could print \\n explicitly if we change "\\n" into "\\n" for every such character... But the problem is that I don't know what is inside unknown1... It is read from a file....

Thanks for answering, however we have further concerns:

The procedure answered has one more porblem... Suppose I don't know that the only possible special character in the file is \\n or \\t... maybe there are something like \\u ?\u003c/i> \\l ? i think we can't exhaust every possibility right? Is there kind of built in C++ function just to output the corresponding characters?

Answer 1

\\n , \\t are escape sequences, but you can print them by adding an extra \\ before them, \\\\ is used to obtain a single backslash. A single backslash means it is an escape sequence ( if it is a valid one ), but two backslashes represent the backslash character, so whenever you need to output a backslash, just add two of them.

So, if you use

string unknown1="\\n\\t\\n\\t\\n\\n\\n\\n\\n";

You will get your desired output.

If you are reading from a file , then do something like this

string unknown1="\n\t\n\t\n\n\n\n\n";
for ( int i = 0 ; i < unknown1.length() ; i++ )
{
    if( unknown1[i] == '\n')
      cout<<"\\n";
}

Like that, you will have to check for each escape sequence that may be used.

Answer 2

Run specific checks for the non-printable characters you are worried about like this.

char c;
while(c!=EOF){
    if(c=='\n')printf("\\n");
    if(c=='\t')printf("\\t");

    and so on and so forth.
    c = the next charater;
}

oops, I wrote C instead of C++ but @Arun AS has the right syntax

Answer 3

See below example. You can add your own characters to the switch to extend the characters it handles.

#include <iostream>
#include <string>

std::string escapeSpecialChars(const std::string& str)
{
    std::string result;

    for(auto c : str)
    {
        switch(c)
        {
            case '\n':
                result += "\\n";
                break;

            case '\t':
                result += "\\t";
                break;

            default:
                result += c;
                break;
        }
    }

    return result;
}

int main()
{
    std::string str = "\n\n\n\t";

    std::cout << escapeSpecialChars(str);

    return 0;
}

Answer 4

You could create your own function to print characters using a std::map:

void printChar( const char ch )
{
  static const std::map< char, std::string > char_map = {
    { '\n', "\\n" }
    // add mappings as needed
  };

  auto found = char_map.find( ch );
  if ( found != char_map.end() )
    std::cout << found->second;
  else
    std::cout << ch;
}

// usage
std::string str = "a\nbc";
for ( auto ch : str ) printChar ( ch );