while getline corrupting the stream

[Gary Wessle]

Hi

please look at the code below, the problem I have is that line 37 does
not print out into the file as expected. however if I move it to be
immediately after line 16 it prints fine into the file. apparently the
while block is doing something wicked and corrupting the stream.
how can I fix this?

thank you


1 #include <fstream>
2 #include <iostream>
3 #include <string>
4
5 /* Reads the value for the lookup string from file, and sets the value in m_pair_status
6 if the value does not exist, create it with a default.
7 */
8 double Grid::status( std::string lookup)
9 {
10 std::string f = "my_file_name";
11 std::fstream iofs( f.c_str(), std::ios::in|std::ios:ut );
12 if (!iofs.is_open())
13 {
14 iofs.open( f.c_str(), stdios_base::in | ios_base:ut |
15 ios_base::trunc );
16 }
17 std::string line, word;
18 double val;
19 bool found_it = false;
20 while( !found_it && getline( iofs, line ) )
21 {
22 std::stringstream ss( line );
23 ss >> word;
24 if( word == lookup )
25 {
26 found_it = true;
27 ss >> val;
28 m_pair_status[lookup] = val;
29 iofs.close();
30 return val;
31 }
32 }
33 // value does not exist, create it with a default
34 if( lookup == "reversals" )
35 {
36 val = 0;
37 iofs << "reversals" << " " << val << std::endl;
38 m_pair_status[lookup] = val;
39 } // add other lookups as needed
40 iofs.close();
41 return val;
42 }

 

[Michael]

please look at the code below, the problem I have is that line 37 does
not print out into the file as expected. however if I move it to be
immediately after line 16 it prints fine into the file. apparently the
while block is doing something wicked and corrupting the stream.
how can I fix this?

This looks fairly wicked to me:

29 iofs.close();

37 iofs << "reversals" << " " << val << std::endl;

Michael

 

[Gary Wessle]

This looks fairly wicked to me:

well, the return statement in line 30 prevents opening a closed stream
if thats what you mean.

 

[Michael]

well, the return statement in line 30 prevents opening a closed stream

if thats what you mean.

My bad. Shouldn't try answering these late in the day.

 

[tony_in_da_uk]

please look at the code below, the problem I have is that line 37 does
not print out into the file as expected. however if I move it to be
immediately after line 16 it prints fine into the file. apparently the
while block is doing something wicked and corrupting the stream.
how can I fix this?
11 std::fstream iofs( f.c_str(), std::ios::in|std::ios:ut );
20 while( !found_it && getline( iofs, line ) )
21 { ....
32 }
33 // value does not exist, create it with a default
34 if( lookup == "reversals" )
35 {
36 val = 0;
37 iofs << "reversals" << " " << val << std::endl;
38 m_pair_status[lookup] = val;
39 } // add other lookups as needed

You're only writing this if the lookup failed, in which case getline
will have hit EOF and set various stream state flags. Consider
clearing some before trying to write. Details should be in
Stroustrup's The C++ Programming Language and various online
resources.