C++ variable type trick...

ArthurHuang · 02-15-2008, 10:17 AM

I have three variables:

string className;
int number=92;
char fileName[10]="Math";

Is that possilbe I connect the int(92) and char[](Math) together?
And save "Math92.txt" into the string varialbe className?

Thanks!

cmnorton · 02-15-2008, 10:30 AM

sprintf should be able to produce a string for you.

You'd have to look at string's member functions to see how string(s) are loaded. Perhaps, string objects allow you pointer access to their internal char buffer. At worst, you'd have an interim char buffer, sprintf the result of your text and integer to that, and then load your string variable from the buffer.

elsheikhmh · 02-15-2008, 11:07 AM

you could this in many ways;
one way is to use sprintf(buf, "%s%d.txt", number, filename) where buf is a char buffer of appropriate size. then assign the contents of buf to className via assignment operator) className = buf
check http://www.cplusplus.com/reference/string/string/

another way is to use stringstream http://www.cplusplus.com/reference/i.../stringstream/
stringstream sstream;
sstream << number << filename << ".txt";
then copy the string buffer into className
className = sstream.str();

-Mustafa

ta0kira · 02-15-2008, 12:06 PM

I'd go with snprintf to keep from overrunning your buffer.

Code:

#include <stdio.h>
#include <string.h>
#include <string>

int main()
{
    std::string className = "class";
    int number=92;
    char fileName[11]="Math";

    snprintf(fileName + strlen("Math"), 11 - strlen("Math"), "%i.txt", number);

    FILE *file = fopen(fileName, "a");

    if (!file) return 1;

    fprintf(file, "%s\n", className.c_str());

    fclose(file);

    return 0;
}

Don't forget space for the terminating \0!
ta0kira

PS Or even better:

Code:

    char fileName[256] = "";
    snprintf(fileName, 256, "Math%i.txt", number);

JWPurple · 02-15-2008, 07:41 PM

c'mon guys, the OP requested C++!

Code:

#include <sstream>

...
string className;
int number=92;
char fileName[10]="Math";

std::ostringstream ostr;

ostr << filename << number << ".txt";
className = ostr.str();
...

Sorry I didn't see elsheikhmh's post, but this is the ONLY way to do this in C++, not "another" way.