how to check a string for specific conditions in C++ - c++

Question

following snippet shows a very small part of my current output:
1464: ebfffe4d bl da0 <memcpy#plt>
14bc: ebfffe37 bl da0 <memcpy#plt>
every line from the output refers to a string. What I want to archieve is, that in this
case only memcpy#plt will be printed once. When a string contains "bl" then the name
within <...> should be printed and only once printed, since the name within <...> is the same
in both cases. Is there a way to get this?
My current code looks as follows:
class CallFunction {
private:
vector<string> content;
public:
CallFunction(vector<string> content) {
this->content = content;
}
void print() {
for(string line: content) {
if(line.find("bl") != std::string::npos
&& line.find("<") != std::string::npos) {
cout << line << endl;
}
}
}
};
int main() {
string fileName = "libndkmod.s";
vector<string> content = readFile(fileName);
CallFunction cf = CallFunction(content);
cf.print();
}
Thanks in advance and kind regards!

Answer 1

We can use a unordered_set to deduplicate the substring, if the same substring has already been printed, then skip it.
This step can be extracted into a single method to follow the single responsibility principle, which is more natural than process the duplication in print function, this work is left for you.
We use unordered_set instead of std::set since unordered_set will be quicker to search.
I have changed the for loop from for(string line: content) into for(const string& line: content), then we avoid a copy of the original string, to improve the performance. Basically, we will prefer to use for(const auto& item:...) for objects except primitive types to avoid a copy.
We store string_view which is introduced in c++17 to avoid copy the sub-string, it will save memory since we avoid unnecessarily copy.
#include <iostream>
#include <string>
#include <unordered_set>
#include <vector>
using namespace std;
class CallFunction {
private:
vector<string> content;
public:
CallFunction(vector<string> content) { this->content = content; }
void print() {
std::unordered_set<std::string_view> mem;
for (const string& line : content) {
auto left_pos = line.find("bl");
auto right_pos = line.find(">");
if (left_pos != std::string::npos && right_pos != std::string::npos) {
std::string_view sub_view = {&line.front() + left_pos,
right_pos - left_pos + 1};
if (mem.count(sub_view)) continue;
mem.insert(sub_view);
cout << line << endl;
}
}
}
};
int main() {
string fileName = "libndkmod.s";
vector<string> content = {
"1464: ebfffe4d bl da0 <memcpy#plt>",
"14bc: ebfffe37 bl da0 <memcpy#plt>",
"14bc: ebfffe37 bl da0 <memcmp#plt>"};
CallFunction cf = CallFunction(content);
cf.print();
}
Online demo