了解C ++ Vecotor

Question

I have a binary file,

FILE *fp;
fp = fopen("file_name.data", "rb");

Which can be successfully read using fread() with the following C code

int S = 8;
int *table = (int*)malloc(S*sizeof(int));
fread(table, S*sizeof(int), 1, fp);

But when I read file to C++ vector, the result is wrong

vector<int> table;
table.resize(S);
fread(&table[0],table.size(), 1, fp);

Is there anything wrong with above code ?.

Answer 1

table.size() returns the number of elements in the std::vector , not the number of bytes. You still need to multiply that by the size of each element, just like you do in the C code.

fread(&table[0],table.size()*sizeof(int), 1, fp);

Answer 2

Your fread should be:-

fread (&table[0], sizeof(vector<int>::value_type), table.size(), fp);
// OR
fread (&table[0], sizeof(int), table.size(), fp);

Answer 3

Both appear to be wrong (although the C version looks like it will work).

See: http://www.tutorialspoint.com/c_standard_library/c_function_fread.htm

Try these:

int S = 8;
int *table = (int*)malloc(S*sizeof(int));
fread(table, sizeof(int), S, fp);

vector<int> table;
table.resize(S);
fread(&table[0], sizeof(int), table.size(), fp);