C++ std::string is empty but full of '\0'

Question

I have a file which contain some numbers, all in one line . I would like to read this file and put this line to a string variable. So as it contains only one line, the getline() method should works only once

But It's not the case. It works twice. I notice that first my string_descriptor contains the number (so it's okey) but after getline take another line and this time it's empty but by looking at the debugger the string contains a lot of \O\ like 10 times.

\O\O\O\O\O\O\O\O\O\O\O\O\O\O\O\

And it bothers me because after I'm doing some processing and because of that my app crashs.

So what I'm doing is the following :

 fs.open (desc.c_str (), std::ios::in); string line; if(!fs.is_open()) { cout<<"\n Cannot open the text.txt file"; } else { std::string string_descriptor; while (!fs.eof ()) { getline( fs , line); if (line != "" && line.find_first_not_of(' ') != std::string::npos && !line.empty()) { string_descriptor = line; std::cout << "String descriptor : " << string_descriptor << std::endl; } } }

So why it happened ? And especially how can I handle that ? I tried to handle that by doing the following but It's still the same :

if (line != "" && line.find_first_not_of(' ') != std::string::npos && !line.empty())

I checked my file and there is no space at the end of the file, so far I know.

Thank you for your help

You should not loop using eof(): stackoverflow.com/questions/5605125/… — Galik
– Galik, Commented Nov 25, 2016 at 14:10
@stark there were an invisible space at the end of the line...Do you know how can i check that for my future processing ? — lilouch
– lilouch, Commented Nov 25, 2016 at 14:24

Vlad from Moscow · Accepted Answer · 2016-11-25 14:15:18Z

1

To avoid the second iteration of the loop change the loop

 while (!fs.eof ()) { getline( fs , line); //...

the following way

 while ( getline( fs , line) ) { //...

Also this condition

if (line != "" && line.find_first_not_of(' ') != std::string::npos && !line.empty())

can look more simpler

if ( line.find_first_not_of(' ') != std::string::npos )

edited Nov 25, 2016 at 14:15

answered Nov 25, 2016 at 14:12

Vlad from Moscow

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10 Comments

lilouch Over a year ago

Thank for the modification but even by changing in this way but still got the same issue...

Vlad from Moscow Over a year ago

@lilouch Maybe the file contains two records and the last one is empty. What is the problem?

lilouch Over a year ago

Actually, my file contains only one line with number and my line variable should contains only the numbers but it seems that it loops again and I got an empty string from line. I don't want that and that's why I used the IF condition...But I still get an empty string with full of \0\

Vlad from Moscow Over a year ago

@lilouch It means that the file contains more than one record and nothing more.

lilouch Over a year ago

Thank for your answer but on my file, I have just one line and not two...that's the thing

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