Question

I write to a text file like so:

void writeText(char* desc){
    FILE * pFile;
    pFile = fopen ("CycleTestInfo.txt","a+");
    fputs (desc,pFile);
    fclose(pFile);
}

I embed this in a for loop and I want to write to the file the loop that I am on:

for(int i=0; i<cycles; i++){
    char* cycle="--NEW CYCLE "+(char)i+"---\r\n";
    writeText(cycle);
}

However, I get error C2110: '+' : cannot add two pointers at the line where I declare cycle. How can I declare the the variable so that I can include the cycle number, i and also add a string to both sides?

Thanks for the help!

Answer 1

That’s not how you concatenate strings in C++.

You can either use sprintf or std::string.

The latter is more C++-ish::

std::string cycle("--NEW CYCLE");
cycle += (char)i;
cycle += "---\r\r";

writeText(cycle.c_str();

Note that you must also change the function signature to:

void writeText(const char* desc)

since string::c_str() returns a const char*.

Or you could use a stringstream, but that’s a bit of overkill in this case. Worth looking into it though.

The reason you’re getting an error is that "--NEW CYCLE " is a const char* in C++, not a std::string.

You could edit your line to work:

const char* cycle= (std::string("--NEW CYCLE ")+(char)i+"---\r\n").c_str();

but I wouldn’t do that. It looks ugly.