stranger "may be used uninitialized in this function [-Wmaybe-uninitialized]" - c++

Question

Any idea? this is the log:
util.h: In function ‘bool BusyBees()’:
util.h:162:17: warning: ‘bestHashBee’ may be used uninitialized in this function [-Wmaybe-uninitialized]
data[1] = x >> 8;
~~^~~~
miner.cpp:512:14: note: ‘bestHashBee’ was declared here
uint32_t bestHashBee;
^~~~~~~~~~~
this is util.h (the function declare):
/** Write a 32-bit unsigned little-endian integer. */
void inline WriteLE32(unsigned char *data, uint32_t x) {
data[0] = x;
data[1] = x >> 8;
data[2] = x >> 16;
data[3] = x >> 24;
}
this is where i use it:
uint32_t bestHashBee;
unsigned char beeNonceEncoded[4];
WriteLE32(beeNonceEncoded, bestHashBee);
std::vector<unsigned char> beeNonceVec(beeNonceEncoded, beeNonceEncoded + 4);
Thanks for any help!

Answer 1

Let's take a look at the code:
uint32_t bestHashBee;
// at this point bestHashBee is an integer, but it could be any integer
// you have not told it what value it should have. It might be 0 it might be
// 2879872. It depends entirely on what was in that memory location before.
unsigned char beeNonceEncoded[4];
// beeNonceEncoded is an array of 4 random chars - they have not been
// initialized to any known value
WriteLE32(beeNonceEncoded, bestHashBee);
// now beeNonceEncoded contains 4 random chars.
std::vector<unsigned char> beeNonceVec(beeNonceEncoded, beeNonceEncoded + 4);
// you've passes bestHashBee to this function - it's a random value
void inline WriteLE32(unsigned char *data, uint32_t x) {
data[0] = x;
// now data[0] contains a random value
//...
}
the compiler is warning you that you haven't initialized bestHashbee - it's unlikely that you want a slightly random value there.
The recommendations from all the commenters are: initialize it.
uint32_t bestHashBee = 100;
would do it. 100 might not be what you want either. Depending on the version of c++ you're using, you could also use
uint32_t bestHashBee{100};