C ++：确定变量是否不包含数据

Question

I've been messing around in C++ a little bit but I'm still pretty new. I searched around a little bit and even using the keywords of exactly the problem I am trying to tackle yields no results. Basically I am just trying to figure out how to tell if a variable has no data. I have a file that my program reads and it searches for a specific character within that file and basically uses delimiters to determine where to store the actual data in a variable. Now I added some comments in the file saying that it should not be edited which has caused me some problems. So I pretty much want to count the number of comments, but I'm not sure how to do it because the way I had it set up was resulting in huge numbers being returned. So I figured I would attempt to fix it with a simple if statement to see if there was any data in the array while it was running the loop, and if there was then simply add +1 to my variable. Needless to say it did not work. Here's the code. And if you know a better way of doing this, by all means please do share.

size_t arySearchData[20];
size_t commentLines[20];
size_t foundDelimiter;
size_t foundComment;
int commentsNum;

foundDelimiter = lineText.find("]");
foundComment = lineText.find("#");

if (foundComment != std::string::npos) {
    commentLines[20] = int(foundComment);

    if (foundComment = <PROBLEM>){
        commentsNum++;
    }
}

So it successfully gets the two comments in my file and recognizes that they are located at the first index(0) in each line but when I tried to have it just do commentsNum++ in my first if statement it just comes up with tons of random numbers, and I am not sure why. So as I said my problem is within the second if statement, I need a void or just a better way to solve this. Any help would be greatly appreciated.

And yes I do realize I could just determine if there 'was' data in the there rather than being void or null but then it would have to be specific and if the comment (#) had a space before it, then it would render my method of reading the file useless as the index will have changed.

Answer 1

A variable in C++ always contains data, just it may not be initialised.

int i;

It will have some value, what it is can't be determined until you do something like

i = 1337;

until you do that the value of i will be what ever happened to be in the memory location that i has been assigned to.

The compile may pick up on the fact that you are trying to use a variable which you have not actually given a value your self, but this will normally just be a warning, as their is nothing wrong as such with doing so

Answer 2

You do not initialize commentsNum. Try this:

int commentsNum = 0;

Answer 3

In C++ other than static variables, other variables are assigned undetermined values. This is primarily done to adhere to underlying philosophy -- "you don't pay for things you don't use", so it doesn't zero that memory by default." However, for static variables, memory is allocated at link time. Unlike runtime initialization, which would need to happen in local variables, link time allocation and initialization incur low cost.

I would recommend hence setting int commentsNum = 0;