skipping line while reading data file

[Ivan Liu]

I would like know how I can skip a line while reading
a set of input data (from a text file) if the first character
of the line is "#".

My original code reads:

ifstream Infile("data.dat");

for( int i=0; i<N; i++){
Infile >x[i] >y[i];
}

[Jerry Coffin]

In article <11**********************@74g2000cwt.googlegroups. com>,
da*******@gmail.com says...

I would like know how I can skip a line while reading
a set of input data (from a text file) if the first character
of the line is "#".

My original code reads:

ifstream Infile("data.dat");

for( int i=0; i<N; i++){
Infile >x[i] >y[i];
}

One obvious possibility would be something like this:

std::istream &my_getline(std::istream &is, std::string &s) {
while (std::getline(is, s) && s[0] == '#')
;
return is;
}

for (int i=0; i<N; i++) {
std::string line;
if (!my_getline(Infile, line))
break;
std::stringstream temp(line);
temp >x[i] >y[i];
}

That does raise one minor question: you're starting with a count (N) of
lines to read. Is that count supposed to include the commented lines or
not? The code above attempts to read N lines of actual data -- if you
want a total of N lines, whether they contain data or not, you'd have to
rewrite it a bit.

--
Later,
Jerry.

The universe is a figment of its own imagination.

[Ivan Liu]

Thanks. I have a further question..
Jerry Coffin wrote:

One obvious possibility would be something like this:

std::istream &my_getline(std::istream &is, std::string &s) {
while (std::getline(is, s) && s[0] == '#')
;
return is;
}

for (int i=0; i<N; i++) {
std::string line;
if (!my_getline(Infile, line))
break;

Is the if-statement for checking if the Infile does exit?

std::stringstream temp(line);
temp >x[i] >y[i];
}

[Jerry Coffin]

In article <11**********************@h48g2000cwc.googlegroups .com>,
da*******@gmail.com says...

[ ... ]

for (int i=0; i<N; i++) {
std::string line;
if (!my_getline(Infile, line))
break;

Is the if-statement for checking if the Infile does exit?

It's mostly to check whether we've reached the end of the file (for
example, if the file got corrupted and only contained one line).

--
Later,
Jerry.

The universe is a figment of its own imagination.