strange problem opening ofstream

[rrsettgast]

Hi all,
I am having a really odd problem. My code is spitting out a bunch of
binary files through ofstream. Actually, I have a little wrapper for
binary ofstream operations....where ofstream is a member of the
wrapper (i.e. not a derived class). At some point during the
execution, my program stops writing output files. The ofstream:pen()
function is failing. The failbit is true. After the fail, I can't even
open a standard ofstream in the same function....but my ofstreams are
fine in other parts of the code. And the kicker is that when I run the
same executable through eclipse's debugger without any breakpoints,
everything works like I think it should. This is above my head. Any
suggestions would be appreciated.

Thanks
Randy
p.s. I am using g++4.2 on OSX.

 

[Daniel T.]

I am having a really odd problem. My code is spitting out a bunch of
binary files through ofstream. Actually, I have a little wrapper for
binary ofstream operations....where ofstream is a member of the
wrapper (i.e. not a derived class). At some point during the
execution, my program stops writing output files. The ofstream:pen()
function is failing. The failbit is true. After the fail, I can't even
open a standard ofstream in the same function....but my ofstreams are
fine in other parts of the code. And the kicker is that when I run the
same executable through eclipse's debugger without any breakpoints,
everything works like I think it should. This is above my head. Any
suggestions would be appreciated.

How many is "a bunch"? Are you sure they are all getting closed properly?

 

[rrsettgast]

Hi,
Like 10.
Yes they are all closed.
I do the following commands:
cout<<" output.is_open() = "<<output.is_open()<<endl;
cout<<" output.fail() = "<<output.fail()<<endl;
cout<<" output.bad() = "<<output.bad()<<endl;
cout<<" output.good() = "<<output.good()<<endl;
before and after the output.open( filename , ios::binary | ios:ut |
ios::trunc ); call.
i get:
before open command
output.is_open() = 0
output.fail() = 0
output.bad() = 0
output.good() = 1
after open command
output.is_open() = 0
output.fail() = 1
output.bad() = 0
output.good() = 0

Any way to tell exactly why the open fails?

Thanks again.

 

[James Kanze]

Like 10.
Yes they are all closed.
I do the following commands:
cout<<" output.is_open() = "<<output.is_open()<<endl;
cout<<" output.fail() = "<<output.fail()<<endl;
cout<<" output.bad() = "<<output.bad()<<endl;
cout<<" output.good() = "<<output.good()<<endl;
before and after the output.open( filename , ios::binary | ios:ut |
ios::trunc ); call.
i get:
before open command
output.is_open() = 0
output.fail() = 0
output.bad() = 0
output.good() = 1
after open command
output.is_open() = 0
output.fail() = 1
output.bad() = 0
output.good() = 0

Any way to tell exactly why the open fails?

Not portably, but on most implementations, reading errno
immediately after the open fails (without any intervening code)
will give a good idea. Something like:

stream.open( filename ) ;
if ( ! stream ) {
int err = errno ;
std::cerr << "open of " << filename << " failed: "
<< strerror( err ) << std::endl ;
}

One note, however: in your original posting, you said you were
outputting binary files. Are you sure ofstream is the right
tool; it does text formatting, not binary (and it seems a bit
overweight if the only function in it you use is write()).

 

[Daniel T.]

Like 10.
Yes they are all closed.
I do the following commands:
cout<<" output.is_open() = "<<output.is_open()<<endl;
cout<<" output.fail() = "<<output.fail()<<endl;
cout<<" output.bad() = "<<output.bad()<<endl;
cout<<" output.good() = "<<output.good()<<endl;
before and after the output.open( filename , ios::binary | ios:ut |
ios::trunc ); call.
i get:
before open command
output.is_open() = 0
output.fail() = 0
output.bad() = 0
output.good() = 1
after open command
output.is_open() = 0
output.fail() = 1
output.bad() = 0
output.good() = 0

Any way to tell exactly why the open fails?

Thanks again.

OK, I just ran a program on OS X using gcc 4 and opened 253 files
simultaneously with no problems. Your going to have to give more details.

Here's what I did:

// in the below I am using some non-standard stuff...
// c_array: is a class implementing a static array that conforms to
// the Random Access Container concept
// for_each: the one I'm using is non-standard. It takes two ranges
// and performs a binary-op on them, then returns the binary-op
// object.
// range: is an iterator over nonnegative integers. I.e., 0, 1, 2, ...

void test( ofstream& output, int i ) {
cout << i << ' ';
assert( output.is_open() == false );
assert( output.fail() == false );
assert( output.bad() == false );
assert( output.good() == true );
stringstream ss;
ss << "foobar " << i << ".txt";
output.open( ss.str().c_str() );
assert( output.is_open() == true );
assert( output.fail() == false );
assert( output.bad() == false );
assert( output.good() == true );
}

int main() {
const int total = 1000;
c_array<ofstream, total> files;
for_each( files.begin(), files.end(), range( total ), &test );
cout << endl;
}

The output:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116
117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134
135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152
153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170
171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188
189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206
207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224
225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242
243 244 245 246 247 248 249 250 251 252 253

failed assertion `output.is_open() == true'

 

[rrsettgast]

Hi,
Thanks for your suggestions. I will try this today. As you have
probably figured out, I am not an engineer first, and a programmer
second. Your suggestion about ofstream being the wrong tool has come
time mind before, but I wouldn't know what else to use...besides a
standard C stream....or just an fstream? So yes i just write binary
files....what would be a more appropriate tool?

Thanks
Randy

 

[James Kanze]

Thanks for your suggestions. I will try this today. As you
have probably figured out, I am not an engineer first, and a
programmer second. Your suggestion about ofstream being the
wrong tool has come time mind before, but I wouldn't know what
else to use...besides a standard C stream....or just an
fstream? So yes i just write binary files....what would be a
more appropriate tool?

A binary stream, not a text stream. There isn't one in the
standard, because there are so many different binary formats.
Implementing one that would be 100% portable can be somewhat
difficult (especially for floating points), but most of the
time, you don't need that degree of portability. (You do still
need to know something about how the iostreams work, since you'd
definitely want to use streambuf and its derived classes, and
probably basic_ios for the error handling as well.)