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Guest
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 Posted: Sun Nov 05, 2006 8:49 pm Post subject: reading struct from file doesn't work subsequent times - hel |
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This code doesn't work - the first retrieval of t2 returns valid data,
the subsequent do not. Please help!!!
int main(int argc, char* argc){
struct Test{
int i;
int j;
intk;
int l;
}
Test Test1;
Test1.i = 99;
Test1.j = 777;
Test1.k = 12345;
Test1.l = 876;
fstream fout;
fout.open("test.txt", ios::out);
for (int i=0; i<10; i++)
fout.write(reinterpret_cast<char*>(&Test1), sizeof(Test));
fout.close();
fstream fin;
fin.open(test.txt", ios::in);
for(int i=0; i<10; i++){
char c[sizeof(Test)];
fin.get(c, sizeof(Test));
Test t2;
// === THIS COPY OF t2 CONTAINS CORRECT DATA FIRST TIME BUT NOT
SUBSEQUENT
// TIMES!!!!!!!!!
memcpy(&t2, c, sizeof(Test));
}
}
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Alberto Ganesh Barbati
Guest
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| Posted: Mon Nov 06, 2006 3:57 am Post subject: Re: reading struct from file doesn't work subsequent times - |
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paul.anderson (AT) jhuapl (DOT) edu ha scritto:
| Quote: | This code doesn't work - the first retrieval of t2 returns valid data,
the subsequent do not. Please help!!!
int main(int argc, char* argc){
struct Test{
int i;
int j;
intk;
int l;
}
Test Test1;
Test1.i = 99;
Test1.j = 777;
Test1.k = 12345;
Test1.l = 876;
fstream fout;
fout.open("test.txt", ios::out);
|
As you are apparently going to write binary data, you should add the
ios::binary flag. BTW, for output-only streams, it usually better to use
ofstream instead of fstream, the difference being that the former
doesn't derive from basic_istream, so you can't apply input operations
by mistake.
| Quote: |
for (int i=0; i<10; i++)
fout.write(reinterpret_cast<char*>(&Test1), sizeof(Test));
fout.close();
fstream fin;
|
Ditto. You should definitely add ios::binary and you could use ifstream
instead of fstream.
| Quote: | fin.open(test.txt", ios::in);
for(int i=0; i<10; i++){
char c[sizeof(Test)];
fin.get(c, sizeof(Test));
|
You should used read(), not get(), up there. get() is meant for textual
input and will stop after extracting a "\n".
| Quote: | Test t2;
// === THIS COPY OF t2 CONTAINS CORRECT DATA FIRST TIME BUT NOT
SUBSEQUENT
// TIMES!!!!!!!!!
memcpy(&t2, c, sizeof(Test));
}
}
|
HTH,
Ganesh
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[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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