CODEWITHSUNDEEP
c++ctimestat
Youssef Korchi
Youssef Korchi

Reputation: 117

C++ convert string to time_t

I'm using stat.st_mtime to get my last modification time of a directory and then store it into a file.txt (stored string is something like that : 1467035651)

Later when I retrieved data from my file.txt, I tried to convert my string from my file.txt to int type since the string contains just seconds but I don't know if it's a good idea to do that.

Is there any way to convert directly to time_t?

Upvotes: 2

Views: 11663

Answers (4)

alk
alk

Reputation: 70931

[Assuming C]

The strto*() family of functions provides fail safe ways to convert a C-"string" to an integer, signed or unsigned, as well as to float and double.

Upvotes: 2

chux
chux

Reputation: 153498

Is there any way to convert directly to time_t?

Various other answers have posted direct solutions with strengths and weaknesses.

contains just seconds but I don't know if it's a good idea to do that.

Answer depends on the goal. IMO, it is the wrong approach

Rather than save/reading as some compiler dependent format, consider using ISO 8601 standards and save the time-stamp in a textual standard version that clearly denotes the time zone, preferable universal time.

Example C code as post is tagged C.
For writing, something like

// Minimum size to store a ISO 8601 date/time stamp
//YYYY-MM-DDThh:mm:ss\0
#define N (4 + 5*3 + 1 + 1)

time_t x;
struct tm *tm = gmtime(&x);
if (tm == NULL) {
  return failure;
}

char dest[N + 1];
int cnt = snprintf(dest, sizeof(dest), "%04d-%02d-%02dT%02d:%02d:%02dZ", 
    tm.tm_year + 1900, tm.tm_mon+1, tm.tm_mday,
    tm.tm_hour, tm.tm_min, tm.tm_sec);
if (cnt < 0 || cnt >= sizeof(dest)) {
  return failure;
}

Additional code need for fractional seconds.
Also see ftime( , , "%FT%T %z", ).

What would you rather read in file.txt? 

1467035651

or 

2016-06-27T13:54:11Z

Upvotes: 2

sighingnow
sighingnow

Reputation: 821

The function atoll in stdlib.h should work. Example:

time_t t;
char *time_string = //...

t = (time_t) atoll(time_string);

Upvotes: 4

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

According to the reference documentation time_t is just an unspecified numeric format.

Just directly read back the numeric value from the file, there's no need for special conversions:

time_t t;
std::ifstream input("File.txt");
// ...
input >> t;

Upvotes: 7

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