Detecting empty line from text file

Question

I have text file like this:

7
a

bkjb
c


dea

hash_table is an array such that line no.-2=index of hash_table array that is every line corresponds to an element in array. The element may be empty line or character like "a\n" which will like this in text file:

a
//empty line

First number is used to decide the size an array hash_table. THe << operator is not treating empty line or '\n' char as string and hence not adding into array. I tried this but no use . Here is my try:

ifstream codes ("d:\\test3.txt"); //my text file

void create_table(int size, string hash_table[]) //creating array
{   string a;
    for(int i=0;i<size;i=i+1)
        {
        codes>>a;
        char c=codes.get();

        if(codes.peek()=='\n')
            {char b=codes.peek();
            a=a+string(1,b);
            }
        hash_table[i]=a;
        a.clear();
        }
}

void print(int size, string hash_table[])
{
    for(int i=0;i<size;i=i+1)
        {if(!hash_table[i].empty())
            {cout<<"hash_table["<<i<<"]="<<hash_table[i]<<endl;} 
        }
}

int main()
{
    int size;
    codes>>size;
    string hash_table[size];
    create_table(size, hash_table);
    print(size, hash_table);



}

NOTE: there can be any no. of empty lines with random sequence.

[`std::getline`](http://en.cppreference.com/w/cpp/string/basic_string/getline) and [`std::string::empty`](http://en.cppreference.com/w/cpp/string/basic_string/empty). — BoBTFish, Oct 28 '13 at 16:39
Note I linked to the `std::string` version, **not** `std::istream::getline` (which should be used rarely to never). — BoBTFish, Oct 28 '13 at 16:40
So your code will be something like `for (; std::getline(file, line); ++lineCount) { if(!line.empty()) table[lineCount]=line; }`. — BoBTFish, Oct 28 '13 at 16:44
I want to include empty line into array. the why `if(!line.empty()) table[lineCount]=line;`? — Nikhil Chilwant, Oct 28 '13 at 16:48
Sorry, I'm doing other things at the same time and not concentrating. The "detecting empty line" in the title made me think that we needed to check that. In which case, if you are including every line sequentially by line number, why aren't you using a `std:vector`? — BoBTFish, Oct 28 '13 at 16:50
You are not being very clear. Detect what? Do you want to store every single line (regardless of if it is blank), and store them indexed by line number? So use a `vector`. — BoBTFish, Oct 28 '13 at 16:53
I want want to store every single line (regardless of if it is blank) — Nikhil Chilwant, Oct 28 '13 at 16:56
So why are you bothering with a hash map rather than a `vector`? — BoBTFish, Oct 28 '13 at 17:01

score 2 · Accepted Answer · answered Oct 28 '13 at 16:44

2

Use std::getline() instead of std::ifstream::operator >>(). The >> operator will skip over whitespace, including newlines.

std::string line;
while (std::getline(codes, line)) {
    //...do something with line
}

answered Oct 28 '13 at 16:44

jxh

64,506
7
96
165

when does this while loop terminates. It should not add EOF to array. – Nikhil Chilwant Oct 28 '13 at 16:51
1

@Nikhil It won't. This is the *correct* way to read every line from a file. If you are ever checking the `eof()` function you are almost certainly doing it wrong. This condition will stop when it tries to read past the last line. – BoBTFish Oct 28 '13 at 16:52
@BoBTFish I did like this [click here](http://codepad.org/HcfqMnaC) but still not working. Compiler stops working without giving any error. See the create_table() fucntion – Nikhil Chilwant Oct 28 '13 at 17:13
works when I delete `hash_table[i]=a;` works fine when I replace it with `cout a;` – Nikhil Chilwant Oct 28 '13 at 17:17
1

@Nikhil: your code sample makes a C-style array of strings and calls it a hash table. What the error is about is the fact that you make it a C-style array with a size that is not known at compile time. Use a std::vector and use .push_back to add new items to the vector. – Klaas van Gend Oct 29 '13 at 08:51

Detecting empty line from text file

1 Answers1