Question

I have got a const char which is made by concatenation like this:

const char *fileName = "background1";

std::stringstream sstm;
sstm << fileName << "-hd.png";
fileName = sstm.str().c_str();

My problem is that the following instruction:

printf("const char = %s size = %d", fileName, sizeof(fileName));

returns:

"const char = background1-hd.png size = 4"

whereas I would expect that it returns:

"const char = background1-hd.png size = 19"

For example, the following gives the convenient result (as there is no concatenation):

const char *fileName2 = "background1-hd";
printf("const char = %s size = %d", fileName2, sizeof(fileName2));

returns:

"const char = background1-hd.png size = 19"

How to avoid this issue and guarantee that the characters will be correctly counted in my concatenated char ?

Thanks !!

Answer 1

sizeof() returns the number of bytes the variable occupies in memory (in this case returns the size of the pointer fileName).

strlen() returns the length of the string (which is what you need).

You could as well try something like:

#include <iostream>
#include <cstdio>

int main()
{
    std::string fileName("background1");
    fileName.append("-hd.png");
    printf("const char = %s size = %d", fileName.c_str(), fileName.length());

    return 0;
}