Cout empty when there are two getline? - c++

Question

I am trying to cout my array but it keep showing empty whenever I try to.
int array_size = 0;
int pos;
string line;
ifstream inFile;
string filename = 'test.txt';
inFile.open(filename);
for(array_size = 0; getline(inFile, line); array_length++);
string * array_holder = new string[array_size];
while(getline(inFile, line))
{
array_holder[pos++] = line;
}
printArray(array_holder, array_size);
Print array
void printArray(string * data, int x)
{
for(int z = 0; z < x; z++)
cout << data[z] << endl;
}
When I comment out this line:
for(array_size = 0; getline(inFile, line); array_length++);
The printArray will show all the contents inside.
But when I uncomment the line, it just show empty lines (depending on the array size).
I reckon this is due to double getline? Do I need to clear the getline buffer or something? I couldn't find any details about getline buffer except for cin. Or is this memory issue?
Note that I cannot use vector in my situation and I need to read the total number of lines in the text file in order to parse the array size to my array syntax.
Thanks.

Answer 1

for(array_size = 0; getline(inFile, line); array_length++);
This loop reads inFile, one line at a time, until the end of the file is reached.
After this loop terminates, the entire file has been read. After all, that's exactly what your program tells your computer to do: read one line at a time, incrementing the counter, until getline fails, which happens at the end of the file. But then immediately afterwards, the second loop attempts to continue reading from the file:
while(getline(inFile, line))
However, since the end of the file has already been reached, this immediately fails, and nothing happens.
You obviously want to reread the file from the beginning, here. However, the Golden Rule Of Computer Programming states "your computer will always do exactly what you tell it to do, instead of what you want it to do". You have not told your computer to go back to the beginning of the file here, so it has no reason to do that. So, you simply have to tell your computer to do that, by closing and reopening the file, or by using the seekg() method.