因为代码要在嵌入式设备上验证日志文件中的最新的n行中有我们需要的日志信息。所以用“文心一言”查了一下读取文件最后n行的方法。
考虑到嵌入式设备上内存不大行，如果文件特别大，全部加载到内存会爆内存，所以设计下面的算法。“文心一言”给的默认代码无法通过编译，本例子解决了他不能解决的问题。可能效率也不太高，还可以在优化。但是凑合用吧。
代码如下，
conanfile.txt

[requires]
nlohmann_json/3.11.3
boost/1.72.0
pybind11/2.12.0

[generators]
cmake

CMakeLists.txt

cmake_minimum_required(VERSION 3.3)


project(51_log_getter)

set(CMAKE_CXX_STANDARD 17)
add_definitions(-g)


include(${CMAKE_BINARY_DIR}/conanbuildinfo.cmake)
conan_basic_setup()

include_directories(${INCLUDE_DIRS} /opt/pyenv/versions/3.7.13/include/python3.7m/)
LINK_DIRECTORIES(${LINK_DIRS} /opt/pyenv/versions/3.7.13/lib/)

file( GLOB main_file_list ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp) 
file( GLOB source_files ${CMAKE_CURRENT_SOURCE_DIR}/*.cc)

foreach( main_file ${main_file_list} )
    file(RELATIVE_PATH filename ${CMAKE_CURRENT_SOURCE_DIR} ${main_file})
    string(REPLACE ".cpp" "" file ${filename})
    add_executable(${file}  ${main_file} ${source_files})
    target_link_libraries(${file}  ${CONAN_LIBS} pthread python3.7m)
endforeach( main_file ${main_file_list})

main.cpp

#include <iostream>
#include <regex>


#include <iostream>  
#include <fstream>  
#include <vector>  
#include <string>  
  
#include <iostream>  
#include <fstream>  
#include <vector>  
#include <string>  
  
std::vector<std::string> read_last_n_lines(const std::string& filename, size_t n) {
    if(n == 0) {
        return {};
    } 

    std::ifstream file(filename, std::ios::binary | std::ios::ate);  
    
    if(!file) {  
        std::cerr << "Could not open file: " << filename << std::endl;  
        return {};  
    }  
      
    std::streamsize size = file.tellg();  
    if (size == 0) {  
        // Empty file  
        return {};  
    }  
            
    // Read from the end of the file towards the beginning  
    size_t bytes_to_read = std::min<std::size_t>(size, 128); // Start with a reasonable buffer size  
    std::streampos file_size = file.tellg(); 
    int start_pos = file_size;
    std::string lines_buffer;
    std::string cur_buffer;

    while(start_pos > 0 && std::count(lines_buffer.begin(), lines_buffer.end(), '\n') < n+1) {
        start_pos = start_pos - bytes_to_read;
        int cur_read = bytes_to_read;
        if(start_pos < 0) {
            start_pos = 0;
            cur_read = start_pos + bytes_to_read;
        } 
        file.seekg(start_pos);
        cur_buffer.clear();
        cur_buffer.resize(cur_read);
        file.read(cur_buffer.data(), cur_buffer.size());
        lines_buffer = cur_buffer + lines_buffer;
    }
    
    // Remove it, just for debugging purpose
    // std::cout << "current buffer: " << std::endl;
    // std::cout << lines_buffer << std::endl;
    // std::cout << "===================end buffer===================" << std::endl;
    
    file.close();

    std::vector<std::string> lines;  
    std::string line;  
    size_t pos = 0;  
      
    // Process the buffer to extract lines  
    while (pos < lines_buffer.size() && lines.size() < n + 1) {  
        size_t newline_pos = lines_buffer.find('\n', pos);  
        if (newline_pos == std::string::npos) {  
            // No more newlines, append the rest of the buffer as one line  
            line += std::string(lines_buffer.begin() + pos, lines_buffer.end());  
            lines.push_back(line);  
            break;  
        } else {
            // Append the current line to the vector  
            line += std::string(lines_buffer.begin() + pos, lines_buffer.begin() + newline_pos);  
            lines.push_back(line);  
            line.clear(); // Reset line for the next iteration  
            pos = newline_pos + 1; // Move to the next character after the newline  
        }  
    } 

    if(lines.size() > 1) {
        lines = std::vector<std::string>(lines.begin() + 1, lines.end());
    }

    return lines;  
}  


int main(int argc, char* argv[]) {
    std::string file_name = "../planning.log";
    auto lines = read_last_n_lines(file_name, 2);
    for(auto const& line: lines) {
        std::cout << line << std::endl;
    }
    std::cout << std::endl;

    return EXIT_SUCCESS;
}

程序输出效果如下，

image.png