Out of bounds with find and replace in C++ - c++

Question

I seem to be running into an odd situation that I do not undersand in C++. When I execute a function that parses and replaces strings (Roman Numerals). I end up going out of bound if the string is not present:
Terminal output:
Mac Shell: CPP/>$ ./Roman2Num
Retrieving input:
------------------
Enter a number: 24
input: XXIV
libc++abi.dylib: terminating with uncaught exception of type std::out_of_range: basic_string
Abort trap: 6
Mac Shell: CPP/>$ ./Roman2Num
Retrieving input:
------------------
Enter a number: 29
input: XXVIV
Roman: XXIX
Mac Shell: CPP/>$ ./Roman2Num
Retrieving input:
------------------
Enter a number: 1999
input: MDCDLXLVIV
Roman: MDCDLXLIX
Mac Shell: CPP/>$ ./Roman2Num
Retrieving input:
------------------
Enter a number: 1998
input: MDCDLXLVIII
libc++abi.dylib: terminating with uncaught exception of type std::out_of_range: basic_string
Abort trap: 6
Mac Shell: CPP/>$
Code written:
string Cleanup(string Roman){
int count = 0;
printf("input: %s\n", Roman.c_str());
size_t w = Roman.find("VIV");
Roman.replace(w, std::string("VIV").length(), "IX");
/* size_t x = Roman.find("LIX");
Roman.replace(x, std::string("LIX").length(), "IL");
size_t y = Roman.find("VIV");
Roman.replace(y, std::string("VIV").length(), "IX");
size_t z = Roman.find("VIV");
Roman.replace(z, std::string("VIV").length(), "IX");*/
return Roman;
}
I have been doing some reading here:
http://www.cplusplus.com/reference/string/string/replace/
Does anyone see what I am doing wrong?
Am I making this way harder than it needs to be?

Answer 1

You need to check for and protect against the "Not Found" condition.
size_t w = Roman.find("VIV");
if (w != string::npos) {
Roman.replace(w, string("VIV").length(), "IX");
}

Answer 2

When the string is not found Romand.find() returns string::npos, which equals (std::string::size_type)-1.
See here: http://www.cplusplus.com/reference/string/string/find/