| Old Zhou has a code chat, where the flowers fall under the keyboard; each line weaves a dream of the galaxy,poetry and code nurture a clear virtue. |
I am Old Zhou! Follow the “Old Zhou Code Chat” public account for more selected content!～ ∞ ～ ∞ Introduction to string ～∞ ～∞ ～
| string is a class in the C++ standard library that handles strings, providing a rich set of functionalities to manipulate strings. This statement may seem vague, but don’t worry, Old Zhou will focus on commonly used aspects in projects… |
～ ∞ ～ ∞ Declaration and Initialization of string～∞ ～∞ ～
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// String.cpp #include <iostream> using namespace std; void initString(){ // Common initializations string s1; string s2(“laoz V5”); string s3 = “laozV5”; string s4 = s3; string s5(s4); cout<<“s1:”<<s1<<endl; cout<<“s2:”<<s2<<endl; cout<<“s3:”<<s3<<endl; cout<<“s4:”<<s4<<endl; cout<<“s5:”<<s5<<endl; // Less common initializations string s6(6, ‘z’); string s7(s3, 1,4); # Starting from the 0th byte, count the next 4 bytes cout<<“s6:”<<s6<<endl; cout<<“s7:”<<s7<<endl; } int main(){ initString(); return 0; } |
| Execution Result:# g++ String.cpp -o String# ./String
s1: s2:laozV5 s3:laozV5 s4:laozV5 s5:laozV5 s6:zzzzzz s7:aozV # The first 4 bytes starting from the first byte of s3 |
～ ∞ ～ ∞ String Add, Delete, Search, and Modify～∞ ～∞ ～
| //String.cpp
#include <iostream> using namespace std; void operatorString(){ // Add cout<<“String add:”<<endl; string s1 = “hello world!”, s2 = “la”; string s3 = s1+” “+s2; // The “+” operator is supported cout<<” s1:”<<s1<<” s2:”<<s2<<” s3:”<<s3<<endl; s3 += ” handsome!”; // The “+=” operator is supported cout<<” s3+=:”<<s3<<endl; s3.insert(8, “oz”); // Insert “oz” at the 8th byte position, shifting the following bytes cout<<” s3.insert():”<<s3<<endl; s3.push_back(‘n’); // Add ‘n’ character to the end of the string, string addition is not supported cout<<” s3 push_back():”<<s3<<endl; // Delete cout<<“\nString remove:”<<endl; s3.erase(0, 5); // Delete the first 5 bytes from position 0 cout<<” s3.erase():”<<s3<<endl; s3.pop_back(); // Delete the last byte cout<<” s3.pop_back():”<<s3<<endl; s3.clear(); // Clear the string cout<<” s3.clear():”<<s3<<endl; // Query cout<<“\nString query:”<<endl; cout<<” s3.empty():”<<s3.empty()<<endl; // Check if the string is empty s3 = s1; cout<<” s3.size():”<<s3.size()<<endl; // C++11, string length cout<<” s3.length():”<<s3.length()<<endl; // Same as size() // Old Zhou’s compiler defaults to allocate 30, can use s3.reserve to allocate cout<<” s3.capacity():”<<s3.capacity()<<endl; cout<<” s3[0]:”<<s3[0]<<endl; // Supports collection-style access cout<<” s3.at(0):”<<s3.at(0)<<endl; // Get the byte at the specified position cout<<” s3.front():”<<s3.front()<<endl; // Get the first byte cout<<” s3.back():”<<s3.back()<<endl; // Get the last byte cout<<” s3:”<<s3<<endl;
// Get 3 bytes starting from the 3rd position cout<<” s3.substr():”<<s3.substr(3,3)<<endl; // Find the position of the specified string from the left cout<<” s3.find():”<<s3.find(“wo”)<<endl; // Find the position of the specified string from the right (returns the position counted from the left) cout<<” s3.rfind():”<<s3.rfind(“wo”)<<endl; // Modify cout<<“\nString modify:”<<endl; s3.replace(2,4, “good”); // Replace 4 bytes starting from the 2nd byte cout<<” s3.replace():”<<s3<<endl; } int main(){ operatorString(); return 0; } |
| Execution Result:# g++ String.cpp -o String# ./String
String add: s1:hello world! s2:la s3:hello world! la s3+=:hello world! la handsome! s3.insert():hello woozrld! la handsome! s3 push_back():hello woozrld! la handsome!n String remove: s3.erase(): woozrld! la handsome!n s3.pop_back(): woozrld! la handsome! s3.clear(): String query: s3.empty():1 s3.size():12 s3.length():12 s3.capacity():30 s3[0]:h s3.at(0):h s3.front():h s3.back():! s3:hello world! s3.substr():lo s3.find():6 s3.rfind():6 String modify: s3.replace():hegoodworld! |
～ ∞ ～ ∞ String Conversion between string and Numeric Values～∞ ～∞ ～
| // String.cpp
#include <iostream> using namespace std; void conversionString(){ // Conversion between numbers and string int i = stoi(“66”); double j = stod(“88.88”); cout<<“stoi():”<<i<<” stod():”<<j<<endl; string s1 = to_string(66); string s2 = to_string(88.88); cout<<“to_string(int):\”” <<s1<<“\” to_string(double):\””+s2<<“\””<<endl; // Conversion between string and char string const char* cstr = s1.c_str(); const char* data = s1.data(); cout<<“s.c_str():\””<<cstr<<“”s.data():\”” <<data<<“\””<<endl; string s3(cstr); cout<<“s3:(cstr):\””<<s3<<“\””<<endl; } int main(){ conversionString(); return 0; } |
| Execution Result:# g++ String.cpp -o String# ./String
stoi():66 stod():88.88 to_string(int):”66″ to_string(double):”88.880000″ s.c_str():”66″ s.data():”66″ s3:(cstr):”66″ |
～ ∞ ～ ∞ String Splitting～∞ ～∞ ～
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// String.cpp #include <iostream> #include <sstream> using namespace std; void splitString(){ // Split string string input = “laoz&laom&laol&laof”; istringstream ss(input); string token; while(getline(ss, token, ‘&’)){ cout<<token<<endl; } // Merge strings ostringstream oss; oss << “my name is “<<“laoz”<<18; string s3 = oss.str(); cout<<“s3:”<<s3<<endl; } int main(){ splitString(); return 0; } |
| Execution Result:# g++ String.cpp -o String# ./String
laoz laom laol laof s3:my name is laoz18 |
～ ∞ ～ ∞ Trimming Spaces from Both Ends of String～∞ ～∞ ～
| // String.cpp
#include <iostream> #include <algorithm> using namespace std; void ltrim(string& s){ // Remove left spaces s.erase(s.begin(), find_if(s.begin(), s.end(), [](unsigned char ch){ return !isspace(ch); } ) ); } void rtrim(string& s){ // Remove right spaces auto it = find_if(s.rbegin(), s.rend(), [](unsigned char ch){ return !isspace(ch); }); s.erase(it.base(), s.end()); } void trim(string& s){ // Remove spaces from both ends ltrim(s); rtrim(s); } int main(){ string s=” laoz hello “; ltrim(s); // Remove left spaces cout<<“s:”<<s[0]<<” s.len:”<<s.length()<<endl; cout<<“s:”<<s<<endl; rtrim(s); // Remove right spaces cout<<“s:”<<s[0]<<” s.len:”<<s.length()<<endl; string s1 = ” laoma hello “; trim(s1); // Remove spaces from both ends cout<<“s:”<<s[0]<<” s.len:”<<s.length()<<endl; return 0; } |
| Execution Result:# g++ String.cpp -o String# ./String
s:l s.len:13 # Result after removing left spaces s:laoz hello s:l s.len:10 # Result after removing right spaces s:l s.len:10 # Result after removing spaces from both ends |
～ ∞ ～ ∞ String Comparison～∞ ～∞ ～
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// String.cpp #include <iostream> using namespace std; void upperLowerCompare(){ string s = “Hello World”; transform(s.begin(), s.end(), s.begin(), ::toupper); // Convert to uppercase cout<<“s upper:”<<s<<endl; transform(s.begin(), s.end(), s.begin(), ::tolower); // Convert to lowercase cout<<“s lower:”<<s<<endl; string s1 = “Laoz”; string s2 = “LAOz”; if(s1.compare(s2) == 0){ // Precise comparison of two strings (including case) cout<<“compare ok!”<<endl; }else{ transform(s1.begin(), s1.end(), s1.begin(), ::toupper); transform(s2.begin(), s2.end(), s2.begin(), ::toupper); if (s1.compare(s2) == 0){ cout<<“compare ok ignore case”<<endl; }else{ cout<<“compare failed”<<endl; } } } int main(){ upperLowerCompare(); return 0; } |
| Execution Result:# g++ String.cpp -o String# ./String
s upper:HELLO WORLD s lower:hello world compare ok ignore case |
Old Zhou: “The foundation is not solid, the earth shakes! Just like in a game, you can’t skip the novice village; you can’t expect to unleash a big move without even knowing how to do a basic attack, right? Skills can be forgotten more cleanly than a first love, but you must chew through the basics like an old workhorse—after all, if the system crashes one day, at least we should be able to manually code a fake Hello World, right?””