Like this:
To use the weight, you sum up the individual m_Weight members, then generate a random number in range 0 - (sum - 1). Then you walk the vector again and subtract each m_Weight from the generated random number; as soon as it becomes negative, you use that item in the vector.
struct cWeightedEnchantment
{
int m_Weight;
cEnchantments m_Enchantments;
};
typedef std::vector<cWeightedEnchantment> cWeightedEnchantments;
To use the weight, you sum up the individual m_Weight members, then generate a random number in range 0 - (sum - 1). Then you walk the vector again and subtract each m_Weight from the generated random number; as soon as it becomes negative, you use that item in the vector.