inserting the \ character into a string

Question

I am tryin to insert a \ charcter into a string so I would get

C:\\Users\\dave\\Desktop\\XY.txt instead of C:\Users\georg\Desktop\XY.txt

here is code but for some reason it does not work

string q="C:\Users\georg\Desktop\XY.txt";
char x='\\';


for (int i = 0; i < q.length(); ++i) {
if (q[i] == '\\')
 q.insert(i,4,x);
 }

Answer 1

Just write

string q="C:\\Users\\georg\\Desktop\\XY.txt";

Or use a raw string literal

string q=R"(C:\Users\georg\Desktop\XY.txt)";

Answer 2

You should use \ within quotes to add a single . So your first line is the problem. It should be

string q="C:\\Users\\georg\\Desktop\\XY.txt";

Then the rest will work.

EDIT

after additional explanation, I found problems with the follow up code. It should be fixed to the following:

for (int i = 0; i < q.length(); ++i) {
    if (q[i] == '\\') {
        q.insert(i,1,x);
        i++;
    }
}

Let me explain, first of all, you need only 1 additional \ so second parameter of insert should be 1. After inserting, you need to skip inserted \, hence i++;

Answer 3

Objective

Add an extra backslash to each one found in the string (for use in another program)

Current issues

1. Example string is not escaped properly (easiest is to use a raw string)
2. The for loop inserts 4 backslashes at a time and so will never reach the end.

Solution with C++11

This will add a backslash to each one that is already there:

#include <iostream>
#include <string>

int main()
{
    std::string q = R"(C:\Users\georg\Desktop\XY.txt)";

    char x='\\';


    for (int i = 0; i < q.length(); ++i) {
        if (q[i] == '\\') {
            q.insert(++i,1,x);
        }

    }
    return 0;
}

Solution without raw strings

#include <iostream>
#include <string>

int main()
{
    //std::string q = R"(C:\Users\georg\Desktop\XY.txt)";
    std::string q = "C:\\Users\\georg\\Desktop\\XY.txt";

    char x='\\';


    for (unsigned i = 0; i < q.length(); ++i) {
        if (q[i] == '\\') {
            q.insert(++i,1,x);
        }
    }

    std::cout << q;

    return 0;
}

Result

C:\\Users\\georg\\Desktop\\XY.txt

Answer 4

The problem is that the first line either needs to be a raw string literal or have \\ in it:

#include <string>
#include <iostream>

using namespace std;

int main()
{
    string q  = R"(C:\Users\georg\Desktop\XY.txt)"; // Raw (C++11 and higher)
    string q2 = "C:\\Users\\georg\\Desktop\\XY.txt"; // Escaped

    cout << q << "\n"   // Outputs: C:\Users\georg\Desktop\XY.txt
         << q2 << "\n"; // Outpits: C:\Users\georg\Desktop\XY.txt
}

As written, it is trying to use \U, \g, etc. as special characters.

---

Update: To actually do what you are asking, you'd want to do something like:

#include <string>
#include <iostream>

using namespace std;

// From http://stackoverflow.com/a/15372760/201787
void replaceAll( string &s, const string &search, const string &replace ) {
    for( size_t pos = 0; ; pos += replace.length() ) {
        // Locate the substring to replace
        pos = s.find( search, pos );
        if( pos == string::npos ) break;
        // Replace by erasing and inserting
        s.erase( pos, search.length() );
        s.insert( pos, replace );
    }
}

int main()
{
    string q = R"(C:\Users\georg\Desktop\XY.txt)"; // Raw (C++11 and higher)
    string q2 = "C:\\Users\\georg\\Desktop\\XY.txt"; // Escaped
    string q3;
    std::cin >> q3; // Does not handle whitespace

    replaceAll( q, "\\", "\\\\" );
    replaceAll( q2, "\\", "\\\\" );
    replaceAll( q3, "\\", "\\\\" );

    cout << q << "\n"
         << q2 << "\n"
         << q3 << "\n";
}

Which prints the following if the user enters C:\Users\georg\Desktop\XY.txt :

C:\\Users\\georg\\Desktop\\XY.txt 
C:\\Users\\georg\\Desktop\\XY.txt
C:\\Users\\georg\\Desktop\\XY.txt