Mohsen Pahlevanzadeh writes:
short unsigned size = 100 - strlen((const char *)name.data());
std::string::data() is not guaranteed to be null-terminated. Undefined behavior. Furthermore, this is overdoing it. name.size() will work much better.
memory = '`'; for (i =0 ;i<size;i++) memory += '`'; tmp->name = name + memory;
You should replace all of the above effort with a simple: tmp->name = name; tmp->name.resize(100, '`');
size = 100 - strlen((const char *)publisher.data()); memory = '`'; for (i =0 ;i<size;i++) memory += '`'; tmp->publisher = publisher + memory;
Same here. tmp->publisher=publisher; tmp->publisher.resize(100, '`');
fseek(bookFilePtr,0L,SEEK_END); fwrite(ptr,408,1,bookFilePtr);
Undefined behavior. std::string is not an char[]. It is a structure.Hint: if you take a look at what sizeof(ptr) tells you, it's not going to be 408 bytes.
while ( fread(bookPtrObj,408,1,bookFilePtr) == 1 ){
But i get the segmentation fault on read each field.
fread() and fwrite() read and write a raw char buffer. char[]. std::string is not a char[]. Internally, std::string is a single pointer to somewhere else in memory, where std::string happens to have dumped the current contents of your string. If you fread() and fwrite() the std::string itself, fread() and fwrite() knows nothing about what it's reading or writing, besides the actual bytes themselves. fread() and fwrite() has no knowledge that those bytes consist of a pointer to somewhere else in memory, where a string is.
If you actually look at what your fwrite() written out, it's binary garbage.To do this properly, you have to manually place everything you want to write out into a single char buffer. std::vector<char> would be an excellent choice:
std::vector<char> buffer; Then, after you filled this buffer with whatever you want to write: fwrite(&buffer[0], buffer.size(), 1, fp);But, if you really want to use C++, rather than C, you should use std::ofstream, instead of FILE *.
Then to read what you previous wrote out, you have to allocate the buffer first, using resize(), then you can read what you want to read, into the newly-allocated buffer.
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