# C++ Profiling with `gprof`

## What is `gprof`?
`gprof` is a GNU profiler that helps analyze where a program spends most of its execution time. It provides function call counts and execution time details.

## Installing `gprof`
```sh
$ sudo apt-get install binutils
```

## Compiling a C++ Program for Profiling
To use `gprof`, compile your program with the `-pg` flag:
```sh
$ g++ -pg -o my_program my_program.cpp
```

## Example C++ Program
Create a file `my_program.cpp` with the following code:
```cpp
#include <iostream>
#include <chrono>
#include <thread>

void slowFunction() {
    std::this_thread::sleep_for(std::chrono::seconds(1));
}

void fastFunction() {
    for (volatile int i = 0; i < 1000000; ++i);
}

int main() {
    for (int i = 0; i < 5; ++i) slowFunction();
    for (int i = 100; i < 200; ++i) fastFunction();
    return 0;
}
```

## Running and Profiling the Program
1. Compile the program:
   ```sh
   $ g++ -pg -o my_program my_program.cpp
   ```
2. Execute the program to generate `gmon.out`:
   ```sh
   $ ./my_program
   ```
3. Analyze the profiling data:
   ```sh
   $ gprof my_program gmon.out > profile.txt
   $ cat profile.txt
   ```

## Understanding the Output
- **Flat Profile**: Shows execution time spent in each function.
- **Call Graph**: Displays function call relationships and their execution time.

## Best Practices for Using `gprof`
- Use `-O2` optimizations but **avoid `-O3`**, which may inline functions and reduce profiling accuracy.
- Profile with realistic input data to get meaningful results.
- Optimize the slowest functions first based on the profiling report.

## Conclusion
`gprof` is a powerful tool for detecting performance bottlenecks in C++ programs. By identifying expensive functions, developers can make targeted optimizations.