Handling Automatic Naming of Files In C++ Sprintf - c++

Question

I am currently writing a program in C++. I want to save a number of files continuously throughout the run of my program. The format of the filename is as such:
char fnameC[sizeof "C:\..._SitTurn_104_c2_00_00_000.bmp"];
- SitTurn is an experiment name
- 104 is an experiment number
These two will be changing after each different run of the program. Currently, my program works like this:
char fnameCVS[sizeof"C:\\Users\\Adam\\Desktop\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_SitTurn_104_c2_02.csv"];
LARGE_INTEGER frequency;
LARGE_INTEGER t1, t2;
double elapsedTime;
SYSTEMTIME comptime;
int main(int argc, char *argv[])
{
GetSystemTime(&comptime);
sprintf_s(fnameCVS, "C:\\Users\\Adam\\Desktop\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_SitTurn_104_c2_%02d.csv", comptime.wDay);
However, I tried this and I can't seem to get it to work. Can anyone help me?
...//rest of code set up
string expName = "SitStand";
string subjNumber = "101";
char fnameCVS[sizeof "C:\\Users\\Adam\\Desktop\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_" + expName + "_" + subjNumber + "_c2_02.csv"];
LARGE_INTEGER frequency;
LARGE_INTEGER t1, t2;
double elapsedTime;
SYSTEMTIME comptime;
int main(int argc, char *argv[])
{
GetSystemTime(&comptime);
sprintf_s(fnameCVS, "C:\\Users\\Adam\\Desktop\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_" + expName + "_" + subjNumber + "_c2_%02d.csv", comptime.wDay);
Since I am using this filename later in the program also, I would like to be able to just rename all files by changing the two strings: expName and subjNumber. Can someone help me explain how I can name my files using a string inputs (e.g. expName and subjNumber), so I only have to rename those corresponding string each time I change the experiment name, or subject number. Thanks!

Answer 1

Try this:
char fnameCVS[MAX_PATH+1];
SYSTEMTIME comptime;
GetSystemTime(&comptime);
sprintf_s(fnameCVS, _countof(fnameCVS), "C:\\Users\\Adam\\Desktop\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_SitTurn_104_c2_%02d.csv", comptime.wDay);
Or this:
#include <string>
#include <sstream>
std::string expName = "SitStand";
std::string subjNumber = "101";
std::string fnameCVS;
SYSTEMTIME comptime;
GetSystemTime(&comptime);
std::ostringstream oss;
oss << "C:\\Users\\Adam\\Desktop\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_" << expName << "_" << subjNumber << "_c2_" << std::setw(2) << std::setfill('0') << comptime.wDay << ".csv";
fnameCVS = oss.str();

Answer 2

You are mixing sprintf and std::string, which is never a good plan. You should either pick to use C's sprintf with char *, or C++'s std::string with std::stringstream.
Your fnameCVS array isn't going to be big enough: you'll take the sizeof of a std::string, which almost certainly will not be what you want.
Option 1: Use only sprintf. Allocate a big-enough string (e.g. char fnameCVS[256]) and use snprintf(fnameCVS, 256, "...Skeleton_%s_%d_c2_%02.csv", ...).
Option 2: Use only string and use a std::stringstream to build your filename.

Answer 3

This is a really bad idea:
char fnameCVS[sizeof"C:\\Users\\Adam\\Desktop\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_RGBDepth_DataAcquisition2013\\Skeleton_SitTurn_104_c2_02.csv"];
The main reason is that it is very difficult to visually inspect whether you have allocated the right number of bytes. Perhaps you make a slight change to the filename later in the sprintf line but then you forget to update this line or you make a typo. Boom, buffer overflow (which may go undetected until it is time to give a presentation).
A secondary bug is that when you use %02d in printf, the 2 is a minimum field width; if the number would require more than 2 digits then it outputs more than 2 digits, causing a buffer overflow. To be safe here you'd need to check that the number is between 0 and 99 before printing it.
Finally, sprintf_s is a non-standard function, there's really no reason to use it instead of sprintf or snprintf.
In C++ the equivalent formatting is a bit more wordy, but leaves no possibility of buffer overflows:
std::string fnameCVS;
// ...
std::ostringstream oss;
oss << "C:\\Users\\whatever...." << std::setw(2) << std::setfill('0')
<< comptime.wDay;
fnameCVS = oss.str();
If you really want to stick with the printf family plus a static char array (note: you can use printf and a dynamically-sized char container) then to make your code safe:
char const my_format[] = "C:\\Users\\whatever.....\\%02d.csv";
char fnameCVS[ sizeof my_format - 2 ]; // "NN" is two chars shorter than "%02d"
// ...
if ( comptime.wDay < 0 || comptime.wDay > 99 )
throw std::runtime_error("wDay out of range");
snprintf(fnameCVS, sizeof fnameCVS, my_format, comptime.wDay);
Your update indicates that you want to compute various other parts of the filename at runtime too; the C++ version that I suggest is easier to extend than the C-with-static-array version where you have to calculate the amount of memory you need by hand.