Notes from C++ Primer
Operations
Operations of string support lots of operations of sequential container.
- string s; define a new empty string object, named s.
- string s(cp); define a new string object, initialized by a C-style string pointed by cp.
- string s(s2); define a new string object initialized by the copy of s2.
- is >> s; read a string splited by space from input stream is, write into s.
- os << s; output the s into output stream os.
- getline(is, s) get a line of string from input stream is, output into s.
- s1 + s2 concatenate string s1 and string s2.
- s1 += s2 concatenate string s2 at the end of string s1.
As the operation of string is almost the same as container, many executions of vector can be replaced like codes below:
string s("Hiya!");
string::iterator iter = s.begin();
while(iter != s.end())
cout << *iter++ << endl; // postfix increment: print old value
Operations only for string
There‘re three base operations supported by string type but container type.
- substr function, return the sub-string of current string object.
- append and replace function, modify string object.
- a series of find function, which is used to find string object.
Operations of sub-string:
- s.substr(pos, n) return a substring of s, from position pos with length n in s.
- s.substr(pos) return a substring of s, from position pos to the end of s.
- s.substr() return a copy of s.
1. substr
We can pass the beginning position pos of ing substring and a counter n which determines the length of substring to function substr to finish returning substring.
string s("hello world");
// return substring of 5 characters starting at position 6
string s2 = s.substr(6, 5); // s2 = world
An alternative way is:
// return substring from position 6 to the end of s string s3 = s.substr(6); // s3 = world
2. append and replace
append function offers an shortcut to insert string at the end of string:
string s("C++ Primer"); // initialize s to "C++ Primer"
s.append(" 3rd Ed."); // s == "C++ Primer 3rd Ed."
// equivalent to s.append(" 3rd Ed.")
s.insert(s.size(), " 3rd ED.");
replace function is a shortcut of deleting some characters and then inserting other contents:
// starting at position 11, erase 3 characters and then insert "4th" s.replace(11, 3, "4th"); // s == "C++ Primer 4th Ed." // equivalent way to replace "3rd" by "4th" s.erase(11, 3); // s == "C++ Primer Ed." s.insert(11, "4th"); // s == "C++ Primer 4th Ed."
Also, we don‘t need to require the length of inserting string is the same as the length of deleting string. Thus we can replace longer or shorter string:
s.replace(11, 3, "Fourth"); // s == "C++ Primer Fourth Ed."
3. find operations of string
string class offers 6 kinds of serarch function. They all return a string::size_type type value indicating the position of match, or return a special value string::npos indicating fail. string class define npos as a value larger than any validate index of string.
- s.find(args) find the first position match with args in s.
- s.rfind(args) find the last position match with args in s.
- s.find_first_of(args) find the first position match with any character in args in s.
- s.find_last_of(args) find the last position match with any character in args in s.
- s.find_first_not_of(args) find the first position of character not belong to args in s.
- s.find_first_not_of(args) find the first position of character not belong to args in s.
The simple accurate search is find function.
string name("AnnaBelle");
string::size_type pos1 = name.find("Anna"); // pos1 == 0
By default, find operation is case sensitive:
string lowercase("annabelle");
pos1 = lowercase.find("Anna"); // pos1 == npos