Invalid conversion from 'char' to 'const char*' - c++

Question

I have a program that generates a single random character, using the randomCharacter function, and random strings, using the randomString function. The latter utilises the former, and breedWithMutation uses randomCharacter to probabilistically mutate a representation of a gene sequence.
#include <ctime>
#include <boost/random.hpp>
typedef boost::mt19937 randAlgorithm;
int mutationsPerGeneration = 100;
double probabilityOfMutation = 0.05;
string potentialAlleles = "abcdefghijklmnopqrstuvwxyz ";
size_t numberOfAlleles = potentialAlleles.size();
double random01(randAlgorithm & engine)
{
boost::uniform_real<double> u01;
return u01(engine);
}
int randomInteger(randAlgorithm & engine, size_t min, size_t max) {
boost::uniform_int<> minmax(min, max);
return minmax(engine);
}
string randomCharacter(randAlgorithm & engine, string charSet, size_t charSetSize) {
return charSet[randomInteger(engine, 0, charSetSize)];
}
string randomString(randAlgorithm & engine, size_t length, string charSet, size_t charSetSize) {
string s;
s.reserve(length);
for (int i = 0; i < length; i++) {
s.append(randomCharacter(engine, charSet, charSetSize));
}
return s;
}
string breedWithMutation(randAlgorithm & engine, string originalGenome, size_t genomeSize) {
string mutatedGenome;
mutatedGenome.reserve(genomeSize);
double mutationDraw;
for (size_t i = 0; i < genomeSize; i++) {
mutationDraw = random01(engine);
if (mutationDraw < probabilityOfMutation) { //The allele undergoes mutation
mutatedGenome.append(randomCharacter(engine, potentialAlleles, numberOfAlleles));
}
else {
mutatedGenome.append(originalGenome[i]);
}
}
return mutatedGenome;
}
However, when I build the application, I get these errors:
main.cpp: In function ‘std::string randomCharacter(randAlgorithm&, std::string, size_t)’:
main.cpp:31:55: error: invalid conversion from ‘char’ to ‘const char*’
main.cpp:31:55: error: initializing argument 1 of ‘std::basic_string<_CharT, _Traits, _Alloc>::basic_string(const _CharT*, const _Alloc&) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]’
main.cpp: In function ‘std::string breedWithMutation(randAlgorithm&, std::string, size_t)’:
main.cpp:53:45: error: invalid conversion from ‘char’ to ‘const char*’
main.cpp:53:45: error: initializing argument 1 of ‘std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::append(const _CharT*) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>, std::basic_string<_CharT, _Traits, _Alloc> = std::basic_string<char>]’
The line numbers in the errors don't line up perfectly, I realise, but the first two errors refer to the only line in randomCharacter, and the third and fourth errors refer to this line: mutatedGenome.append(originalGenome[i]); in breedWithMutation. What is causing this error?

Answer 1

In C++, char and string are distinctly different types. One cannot implicitly convert a char value to a string (as you are trying to do in randomCharacter).
You could change the return type of randomCharacter to be char instead of string, though that may require changes elsewhere too (I haven't reviewed your code in detail).

Answer 2

Change the return type of randomCharacter() to char.

Answer 3

It's not an invalid conversion to const char, it's an invalid conversion to const char*. Strings in plain C are just arrays of characters, or const char*s. So, you're using a single character where you should be using a string.
To examine one instance: You've set up randomCharacter() to return a C++ string, but in actuality, you're trying to return a single character from charSet. It makes more sense to me for you to make the function return a char, but that's your decision to make.