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What causes printf() to output strange characters to the console when escape sequences are used?

January 14, 2025

I am writing a simple function for use in one of my utility implementation files. I recently discovered–while using one of the C++17 libraries–that outputting directory entries using the std::filesystem::path::string() function inside a call to printf() only results in a string of odd characters being sent to STDOUT. Using cout results in no issue. Here is the code:

    if( !initialized )
    {
        try
        {
            const filesystem::path MODELS_DIRECTORY = R"(C:\-----\-----\-----\models)";
            const filesystem::path RESOURCES_DIRECTORY = filesystem::relative(R"(\Resources)", MODELS_DIRECTORY);

            for( const filesystem::directory_entry& dir_entry : filesystem::directory_iterator{ MODELS_DIRECTORY } )
            {
                string test = "this\\is\\a test\\";
                string directory = dir_entry.path().string();
                printf("%s\n", test);
                //cout << directory << endl;
            }
        }
        catch( filesystem::filesystem_error& fs_err )
        {
            printf( "fs exception caught in GraphicsDataCatalog::InitCatalog()" );
        }
        initialized = true;
    }

Using the testing mechanism composed of std::string test and the call to printf() shows that the double backslashes are culprit. Erasing the space in the string does not solve the issue–I assume perhaps there is a format specifier to resolve the erratic characters printed to the console. Using cout with the string returned by the dir_entry.path().string() call results in success.

Does anyone have more knowledge on the subject?

MRE (Minimally reproducible example):

#include <iostream>

using namespace std;

int main()
{
    const string PASS_STRING = "This is a test.";
    const string FAIL_STRING = "This\\is not\\a\\test.";

    cout << PASS_STRING << endl;
    cout << "Test passed.\n" << endl;

    printf( "%s\n", FAIL_STRING );
    printf( "Test failed.\n" );

    return 0;
}