c++ Function to add an extra '\' to a filepath? - c++

Question

I have about 3500 full file paths to sort through (ex. "C:\Users\Nick\Documents\ReadIns\NC_000852.gbk"). I just learned that c++ does not recognize the single backslash when reading in a file path. I have about 3500 file paths that I am reading in so it would be overly tedious to manually change each one.
I have this for loop that finds the single backslash and inserts a double backslash at that index. This:
string line = "C:\Users\Nick\Documents\ReadIns\NC_000852.gbk";
for (unsigned int i = 0; i < filepath.size(); i++) {
if(filepath[i] == '\') {
filepath.insert(i, '\');
}
}
However, c++, specifically on c::b, does not compile because of the backslash character. Is there a way to add in the extra backslash character with a function?
I am reading the filepaths in from a text file, so they are being read into the string filepath variable, this is just a test.

Answer 1

Use double backslash as '\\' and "C:\\Users...". Because single backslash with the next character makes an escape.
Also the string::insert() method's 2nd argument expects number of characters, which is missing in your code.
With all those fixes, it compiles fine:
string filepath = "C:\\Users\\Nick\\Documents\\ReadIns\\NC_000852.gbk";
// ^^ ^^ ^^ ^^ ^^
for (unsigned int i = 0; i < filepath.size(); i++) {
if(filepath[i] == '\\') {
// ^^
filepath.insert(i, 1, '\\');
} // ^^^^^^^
}
I am not sure, how above logic will work. But below is my preferred way:
for(auto pos = filepath.find('\\'); pos != string::npos; pos = filepath.find('\\', ++pos))
filepath.insert(++pos, 1, '\\');
If you had only single character to be replaced (e.g. linux system or probably supported in windows); then, you may also use std::replace() to avoid the looping as mentioned in this answer:
std::replace(filepath.begin(), filepath.end(), '\\', '/');
I assumed that, you already have a file created which contains single backslashes and you are using that for parsing.
But from your comments, I notice that apparently you are getting the file paths directly in runtime (i.e. while running the .exe). In that case, as #MSalters has mentioned, you need not worry about such transformations (i.e. changing the backslashes).

Answer 2

The problem that you're seeing is because in C++, string literals are commonly enclosed in "" quotes. This brings up one minor problem: how do you put a quote inside a string literal, when that quote would end the string literal. The solution is escaping it with a \. This can also be used to add a few other characters to a string, such as \n (newline). And since \ now has a special meaning in string literals, it's also used to escape itself. So "\\" is a string containing just one character (and of course a trailing NUL).
This also applies to character literals: char example[4] = {'a', '\\', 'b', 0} is an alternative way to write "a\\b".
Now this is all about compile time, when the compiler needs to separate C++ code and string contents. Once your executable is running, a backslash is just one char. std::cout << "a\\b" prints a single backslash, because there's only one in memory. std::String word; std::cin >> word will read a single word, and if you enter one backslash then word will contain one backslash. The compiler isn't involved in that.
So if you read 3500 filenames from a std::ifstream list_of_filenames and then use that to create a further 3500 std::ifstreams, you only need to worry about backslashes in specifying that very first filename in code. And if ou take that filename from argv[1] instead, you don't need to care at all.

Answer 3

One way to get rid of special handling of backslash is to keep all file names in a separate disk file as such and use file stream objects such as ifstream to get file names in C++ format.
TCHAR tcszFilename[MAX_PATH] = {0};
ifstream ObjInFiles( "E:\\filenames.txt" );
ObjInFiles.getline( tcszFilename, MAX_PATH );
ObjInFiles.close();
Suppose first file name stored in filenames.txt is "e:\temp\abc.txt" then after executing getline() above, the variable tcszFilename will hold "e:\\temp\\abc.txt".