问题
I've gone over many questions with the same or similar titles, I have changed the code in so many ways I can't even count.... I have an interesting problem.
I have a class for logging that is extremely simple and just writes stuff into a file. The exact same code works in the constructor, but will not work in the member function. I'm stripping out some irrelevant code, the rest is:
private:
std::string logfile_path_;
std::string program_name_;
std::string GetTimestamp() {
timeval tv;
gettimeofday(&tv, NULL);
char cTimestamp[24];
strftime(cTimestamp, sizeof(cTimestamp), "%F %T", std::localtime(&tv.tv_sec));
sprintf(&cTimestamp[19], ".%03d", (tv.tv_usec / 1000)); // write the miliseconds (microseconds/1000) into cTimestamp starting at the 20th character. %03d == pad with 0, for a minimum length of 3, an integer.
return cTimestamp; // function returns std::string so this will be implicitly cast into a string and returned.
}
public:
int log_level_;
SrxDsLog(std::string Logfile_path, std::string program_name, int log_level) {
log_level_ = log_level;
program_name_ = program_name;
logfile_path_ = Logfile_path;
std::ofstream logfile(logfile_path_.c_str(), std::ios::out | std::ios::app);
std::cout << "Logger started, Log file: " << logfile_path_ << std::endl;
logfile << "Logger started, Log file: " << logfile_path_ << std::endl;
return;
}
void WriteLog(std::string Log_message, int Severity = LOG_CRITICAL, std::string Function_name = "") {
if (Severity >= log_level_) {
std::cout << GetTimestamp() << "|" << program_name_ << "|" << Function_name << "|" << GetSeverity(Severity) << "|" << Log_message << std::endl;
std::ofstream logfile(logfile_path_.c_str(), std::ios::out | std::ios::app);
logfile << GetTimestamp() << "|" << program_name_ << "|" << Function_name << "|" << GetSeverity(Severity) << "|" << Log_message << std::endl;
}
}
The question is why is it working in the constructor, but the exact same code is not working in the member function. The std::cout is writing the exact same log message I want, but it's not appearing in the file. The file contains a single line every time the program is run.
回答1:
In an amazingly unsatisfying turn of events I voted to close my question.
The problem was apparently caused by undefined behavior in unrelated code. And that because I did something that's defined in C++11 but is not in C++03. Apparently you can't call constructors from constructors in C++03....
Because of that, and because the question didn't include the code that was actually at fault, the question seems incredibly bad.
Please close.
回答2:
int log_level_;
The constructor fails to initialize this class member.
Subsequently, the comparison with this class member results in undefined behavior.
来源：https://stackoverflow.com/questions/46370438/stdofstream-wont-write-to-file-sometimes