Question

I got code that follows:

char* writeSpace(int i)
{
 fputs("                              " + (30-i), stdout);
}

printf("#%i key: %s%svalue: %s%s value2: %s", id, key, writeSpace(10), value, writeSpace(8), value2);

my output should look something like:

#1 key: foo          value: bar        value2: foobar

but it isn’t. it looks like:

                      #1 key: foo(null)value: bar(null)value2: foobar(null)

What’s wrong with my code?

Answer 1

Well, you’re fputting all those spaces to the console, so you get them first.

Then you’re outputting everything else, so you get that next.

Perhaps you meant for writeSpace to return a C-style string, rather than print it to the console.

But be sure that you allocate space for it! Since ownership of memory buffers gets a bit hinky, it’s best to allocate space outside of the function.

void writeSpace(char* buf, int i) {
   fputs("                              " + (30-i), buf);
}

char spaceBuf1[30];
writeSpace(spaceBuf1, 10);

char spaceBuf2[30];
writeSpace(spaceBuf2, 8);

printf("#%i key: %s%svalue: %s%s value2: %s",
   id, key, spaceBuf1, value, spaceBuf2, value2);

And consider using actual C++ features like iostreams and std::string. It’ll be much easier:

std::cout << "#" << id << " "
          << " key: " << std::setw(30) << key
          << " value: " << std::setw(30) << value
          << " value2: " << value2;

I recommend these resources for learning idiomatic C++.