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C++ string error with “find_first_of” function

I want to get the word which is between two quotes so im using std::string::find_first_of
but pos2 and pos1 are same values , it causes error.

std::string ss="<tag2 name = "Name1">";
std::size_t pos1=ss.find_first_of(""");
std::size_t pos2=ss.find_first_of(""",pos1);//i'am using pos1 as a base position to get pos2.
std::cout<<pos1<<std::endl<<pos2;


3 Answers
3

You misunderstand the second parameter to find_last_of. It is the last character to be searched. So you just end up finding the same character again. Remove the second parameter and your code will work

find_last_of

std::string ss="<tag2 name = "Name1">";
std::size_t pos1=ss.find_first_of(""");
std::size_t pos2=ss.find_last_of(""");
std::cout<<pos1<<std::endl<<pos2<<std::endl;


According to reference
, second parameter is not position to start searching from, but position to end on.

pos -
Position of the last character in the string to be considered in the search.
Any value greater than, or equal to, the string length (including string::npos) means that the entire string is searched.
Note: The first character is denoted by a value of 0 (not 1).

In your case, you can simply drop second argument and you'll recieve correct position in pos2

pos2

To find the next occurence of " after position pos1, you can use ss.find_first_of('"',pos1+1);

ss.find_first_of('"',pos1+1);

ss.find_last_of('"',pos1); will look for a quote starting at the first quote you found but looking backwards/towards the beginning of the string. You can use ss.find_last_of('"'); to find the last occurence of a quote in the whole string.

ss.find_last_of('"',pos1);

ss.find_last_of('"');

In your example, ss.find_first_of('"',pos1+1); and ss.find_last_of('"'); will yield the same result because the string contains two quotes and therefore, the second quote is also the last quote.

ss.find_first_of('"',pos1+1);

ss.find_last_of('"');

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