The analyzer has detected a potential error related to data incompatibility between the 32-bit and 64-bit versions of an application, when memsize-variables are being written to or read from the stream. The error is this: data written to the binary file in the 32-bit program version will be read incorrectly by the 64-bit one.
For example:
std::vector<int> v;
....
ofstream os("myproject.dat", ios::binary);
....
os << v.size();The 'size()' function returns a value of the size_t type whose size is different in 32-bit and 64-bit applications. Consequently, different numbers of bytes will be written to the file.
There exist many ways to avoid the data incompatibility issue. The simplest and crudest one is to strictly define the size of types being written and read. For example:
std::vector<int> v;
....
ofstream os("myproject.dat", ios::binary);
....
os << static_cast<__int64>(v.size());A strictly defined cast to 64-bit types cannot be called a nice solution, of course. The reason is that this method won't let the program read data written by the old 32-bit program version. On the other hand, if data are defined to be read and written as 32-bit values, we face another problem: the 64-bit program version won't be able to write information about arrays consisting of more than 2^32 items. This may be a disappointing limitation, as 64-bit software is usually created to handle huge data arrays.
A way out can be found through introducing a notion of the version of saved data. For example, 32-bit applications can open files created by the 32-bit version of your program, while 64-bit applications can handle data generated both by the 32-bit and 64-bit versions.
One more way to solve the compatibility problem is to store data in the text format or the XML format.
Note that this compatibility issue is irrelevant in many programs. If your application doesn't create projects and other files to be opened on other computers, you may turn off the V128 diagnostic.
You also shouldn't worry if the stream is used to print values on the screen. PVS-Studio tries to detect these situations and avoid generating the message. False positives are, however, still possible. If you get them, use one of the false positive suppression mechanisms described in the documentation.
Additional features
According to users demand, we added a possibility to manually point out functions, which saves or loads data. When somewhere in code a memsize-type is passed to one of these functions, this code considered dangerous.
Addition format is as follows: just above function prototype (or near its realization, or in standard header file) user should add a special comment. Let us start with the usage example:
//+V128, function:write, non_memsize:2
void write(string name, char);
void write(string name, int32);
void write(string name, int64);
foo()
{
write("zz", array.size()); // warning V128
}Format:
Warning level in case of user functions is always first.
At last, here is full usage example:
// Warns when in method C of class B
// from A namespace memsize-type value
// is put as a second or third argument.
//+V128,namespace:A,class:B,function:C,non_memsize:3,non_memsize:2