sprintf equivalent for the string class <string>

[emaghero]

Morning all,

I am currently processing some data that is contained in several files in several different locations. The filenames contain descriptions of the data that I am working with, for example rect_W_7.2_H_3.8.txt

I am using the STL string class on MSVS to name the directories storing the files.

string drive="c:\\"
string dir1="Output_Files\\";
string dir2="Calculation_Data\\";
string wg1="Rectangular\\";
string loc=drive.append(dir1).append(dir2);
 

Thus far I have been using sprintf_s to open the file that I want to work on, for example

char file[100];
 
sprintf_s(file,100,rect_W_%0.1f_H_%0.1f.txt,width,height);
 
string current=loc;
 
current.append(file);
 
ofstream data.open(current);
 
 

This works fine and I havn't had any problems with it.

I was wondering if there was a sprintf equivalent for strings. Since I will be working with files of variable name length I don't want to have to count into the filename and find the position of %0.1f and use insert every time.

Thanks

[Banfa]

The equivilent is to use a stringstream which work much like cout/cin or any other file stream something like

#include <sstream>
#include <iomanip>
 
...
 
ostringstream ss;
 
ss << loc << "rect_W_" << fixed << setprecision(1) << width << "_H_"  << fixed << setprecision(1) << height << ".txt";
 
current = ss.str();
 

[emaghero]

@Banfa
Cheers, thanks very much.

[emaghero]

@Banfa
On a related note,

Suppose I want to open a binary file for import / export using

int file;
errno_t err=_sopen_s(&file,overlapfile,_O_BINARY,_SH_DENYNO,_S_IREAD);
 
if(file==-1){
    perror("Failed to open file");
}
else{
    //Import data
}
 

The parameter overlapfile is of type

const char *

Is there a way to convert a string to this type after overlapfile has been declared as

char overlapfile[500];
 

or

char *overlapfile;
 

I have tried various approaches, the latest being

string f1;
//Assign something to f1
 
char *overlapfile=new(char[static_cast<int>(f1.size())]);
 
for(int i=0;i<static_cast<int>(f1.size());i++) overlapfile[i]=f1[i];
 

this works but you get some junk at the end of overlapfile.

[emaghero]

@emaghero
Just found a really easy way to get this done

char *overlapfile;
 
overlapfile=(char *)(f1.c_str());
 

Thanks for all the help.

[Banfa]

Good :D

The thing to remember is that all this basic C stuff is required by C++ too so there is nearly always a way to do it through the C++ standard library and STL

[weaknessforcats]

This code is dangerous:

char *overlapfile; 
 
overlapfile=(char *)(f1.c_str()); 

The basic_string<char>::c_str() function returns a const char* so you can't use that pointer to hack into the string.

The user of overlapfile sees it as a char* and if that user tries to change the string pointed at by overlapfile a run-time crash will occur.

overlapfile should be defined as a const char* and there should be no cast.