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V780. The object of non-passive (non-PDS) type cannot be used with the function.
The analyzer detected a dangerous use of composite types. If an object is not a Passive Data Structure (PDS), you cannot use low-level functions for memory manipulation such as 'memset', 'memcpy', etc., as this may break the class' logic and cause a memory leak, double release of the same resource, or undefined behavior.
Classes that cannot be handled that way include std::vector, std::string, and other similar containers.
This diagnostic can sometimes help to detect typos. Consider the following example:
struct Buffer {
std::vector<char>* m_data;
void load(char *buf, size_t len) {
m_data->resize(len);
memcpy(&m_data[0], buf, len);
}
};The 'memcpy' function copies data to the object pointed to by 'm_data' instead of the container. The code must be rewritten in the following way:
memcpy(&(*m_data)[0], buf, len);An alternative version:
memcpy(m_data->data(), buf, len);This error also appears when using memset/memcpy with structures whose fields are non-PDS objects. Consider the following example:
struct Buffer {
std::vector<char> m_data;
....
};
void F() {
Buffer a;
memset(&a, 0, sizeof(Buffer));
....
}We recommend using value initialization to avoid errors like that. This technique works correctly both with POD-data and objects with a non-trivial constructor.
To copy the data, you can use the copy constructor generated by the compiler or write one of your own.
The analyzer also looks for structures that can be dangerous when using memset/memcpy with them because of their logic or the way they are represented in memory. The first case deals with classes that include pointers, constructors, and destructors at once. If a class performs non-trivial pointer handling (for example, memory or resource management), you cannot use memcpy/memset with it. For example:
struct Buffer {
char *buf;
Buffer() : buf(new char[16]) {}
~Buffer() { delete[] buf; }
};
Buffer buf1, buf2;
memcpy(&buf1, &buf2, sizeof(Buffer));The second case deals with classes that are not standard-layout:
struct BufferImpl {
virtual bool read(char *, size_t) { return false; }
};
struct Buffer {
BufferImpl impl;
};
Buffer buf1, buf2;
memcpy(&buf1, &buf2, sizeof(Buffer));This diagnostic is classified as:
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You can look at examples of errors detected by the V780 diagnostic. |
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