strange file reading problem in c++: fread()

0
votes

I have a very strange problem when reading a binary file.

void metaDataProcess(FILE *f){

    unsigned __int32 obLength;
    unsigned __int32 numProp;
    char* objPath;
    unsigned __int32 rawDataIndex;
    int level;
    fread(&obLength,sizeof(obLength),1,f);
    objPath=new char[obLength];
    cout<<"i am at"<<ftell(f)<<endl;
    fread(&objPath,sizeof( char),obLength,f);
    objPath[obLength]='\0';
    cout<<"i am at"<<ftell(f)<<" the object path is "<<objPath<<endl;
level=getOrCreateNode(objPath);

fread(&rawDataIndex,sizeof(rawDataIndex),1,f);

the "objPath" didnt get what is expected in that location. In 010 editor, for that location it is '/', but i read it as '>'. it is quite strange, since from the print out value of ftell, it is the correct position and the value read before and after that are got expected value(obLength=1; and next value rawDataIndex==4294967295).

how come i got '>' when i expceted '/'. i tried fread(&objPath,sizeof(unsigned char),obLength,f); fread(&objPath,1, obLength,f); they are all '>'; can anyone help me with it? thanks

3
c++cfile-io
Is there any particular reason you're not using an ifstream? This isn't very C++-y – Cogwheel
Pick a language to tag your question, either C or C++. You will get better answers. – Sam Miller
Since, later on i will do a real time streaming for this file. i am not sure if the filestream will work or that for that. – Grey
@Sam This is equally applicable to both. – anon
__int32 is not a standard type nor a valid type you can declare yourself (anything beginning with __ is reserved). C has perfectly standard uint32_t and int32_t (and so on) which you should be using. – R.. GitHub STOP HELPING ICE

3 Answers

1
votes
objPath=new char[obLength + 1];
cout<<"i am at"<<ftell(f)<<endl;
fread(objPath,sizeof( char),obLength,f);
objPath[obLength]='\0';
1
votes

I can't see anything wrong with the code above, except that you are acessing an ilegal memory position, since you allocate:

objPath=new char[obLength];

and then do:

objPath[obLength]='\0';

You should have allocated new char[obLength+1] to reserve enough space for the '\0'.

The other thing is that you are printing the result of ftell after reading the file. Is that what you want really?

0
votes

Is your 010 editor showing position in hex rather than decimal? You're programmatically printing it in decimal so that could account for the difference you're seeing.

EDIT: What does your file look like? Is the < one character off from the / you expect? Have you tried reading the characters one at a time and finding out which offset the / actually exists at?