Mixing
c-time function returns strange values
0
I'm working with a code in C, which gets the time from a server using the following:
(This is a very short version, other sections and functions of the code use time, ftime and localtime functions to get the time).
struct tm *stiempo;
long ltiempo;
FILE * arch2;
int main()
{
print_error_time();
}
void print_error_time()
{
time (<iempo);
stiempo = localtime (<iempo);
fprintf (arch2, "%02.2ld/%02.2ld/%02.2ld, t %02.2ld:%02.2ld:%02.2ld", stiempo->tm_mday, (stiempo->tm_mon + 1), (stiempo->tm_year + 1900), stiempo->tm_hour, stiempo->tm_min, stiempo->tm_sec);
}
Sometimes it works just fine, but sometimes, when the time is printed into the file, i get something like this:
21/08/2018, 15:48:7956003943165722682
21/08/2018, 15:50:7956003943165722667
21/08/2018, 15:51:7956003943165722649
Does anyone knows what could be causing this beheaviour or what could affect the time functions that makes them return those values?
c time localtime
asked Jan 2 at 19:31
FaustoFausto
31
add a comment |
0
I'm working with a code in C, which gets the time from a server using the following:
(This is a very short version, other sections and functions of the code use time, ftime and localtime functions to get the time).
struct tm *stiempo;
long ltiempo;
FILE * arch2;
int main()
{
print_error_time();
}
void print_error_time()
{
time (<iempo);
stiempo = localtime (<iempo);
fprintf (arch2, "%02.2ld/%02.2ld/%02.2ld, t %02.2ld:%02.2ld:%02.2ld", stiempo->tm_mday, (stiempo->tm_mon + 1), (stiempo->tm_year + 1900), stiempo->tm_hour, stiempo->tm_min, stiempo->tm_sec);
}
Sometimes it works just fine, but sometimes, when the time is printed into the file, i get something like this:
21/08/2018, 15:48:7956003943165722682
21/08/2018, 15:50:7956003943165722667
21/08/2018, 15:51:7956003943165722649
Does anyone knows what could be causing this beheaviour or what could affect the time functions that makes them return those values?
c time localtime
asked Jan 2 at 19:31
FaustoFausto
31
arch2FILEpointer is not pointing to anyFILEobject.
– H.S.
Jan 2 at 19:40
1
You are using wrong format specifier infprintf(), which is undefined behavior.
– H.S.
Jan 2 at 19:42
Most of the fields in thestruct tmare notlongbutintand printing them with%ldon a 64-bit machine leads to unpredictable behaviour. You could use%.2dor%02dto get your desired result (probably), though maybe you should use 4 instead of 2 for the year (though it does no damage with 2). On a 32-bit machine, you might get away with assizeof(int) == sizeof(long). Also, Win64 might be OK for the sam reason.
– Jonathan Leffler
Jan 2 at 19:48
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:28
@Fausto: the trouble with undefined behaviour is that the code is allowed to work as expected and to work other than as expected, and both are correct because the official requirement is undefined. One way that you can see it working on Machine A and failing on Machine B is if Machine A is 32-bit and Machine B is 64-bit. You could also run into issues if the working machine is Windows 64-bit and the non-working machine is not. And you could run into issues if the CPU on one machine is little-endian and on the other big-endian. You've not identified how similar your two machines are.
– Jonathan Leffler
Jan 4 at 8:41
add a comment |
0
0
0
I'm working with a code in C, which gets the time from a server using the following:
(This is a very short version, other sections and functions of the code use time, ftime and localtime functions to get the time).
struct tm *stiempo;
long ltiempo;
FILE * arch2;
int main()
{
print_error_time();
}
void print_error_time()
{
time (<iempo);
stiempo = localtime (<iempo);
fprintf (arch2, "%02.2ld/%02.2ld/%02.2ld, t %02.2ld:%02.2ld:%02.2ld", stiempo->tm_mday, (stiempo->tm_mon + 1), (stiempo->tm_year + 1900), stiempo->tm_hour, stiempo->tm_min, stiempo->tm_sec);
}
Sometimes it works just fine, but sometimes, when the time is printed into the file, i get something like this:
21/08/2018, 15:48:7956003943165722682
21/08/2018, 15:50:7956003943165722667
21/08/2018, 15:51:7956003943165722649
Does anyone knows what could be causing this beheaviour or what could affect the time functions that makes them return those values?
c time localtime
asked Jan 2 at 19:31
FaustoFausto
31
I'm working with a code in C, which gets the time from a server using the following:
(This is a very short version, other sections and functions of the code use time, ftime and localtime functions to get the time).
struct tm *stiempo;
long ltiempo;
FILE * arch2;
int main()
{
print_error_time();
}
void print_error_time()
{
time (<iempo);
stiempo = localtime (<iempo);
fprintf (arch2, "%02.2ld/%02.2ld/%02.2ld, t %02.2ld:%02.2ld:%02.2ld", stiempo->tm_mday, (stiempo->tm_mon + 1), (stiempo->tm_year + 1900), stiempo->tm_hour, stiempo->tm_min, stiempo->tm_sec);
}
Sometimes it works just fine, but sometimes, when the time is printed into the file, i get something like this:
21/08/2018, 15:48:7956003943165722682
21/08/2018, 15:50:7956003943165722667
21/08/2018, 15:51:7956003943165722649
Does anyone knows what could be causing this beheaviour or what could affect the time functions that makes them return those values?
c time localtime
c time localtime
asked Jan 2 at 19:31
FaustoFausto
31
asked Jan 2 at 19:31
FaustoFausto
31
asked Jan 2 at 19:31
FaustoFausto
31
asked Jan 2 at 19:31
FaustoFausto
31
asked Jan 2 at 19:31
FaustoFausto
31
31
arch2FILEpointer is not pointing to anyFILEobject.
– H.S.
Jan 2 at 19:40
1
You are using wrong format specifier infprintf(), which is undefined behavior.
– H.S.
Jan 2 at 19:42
Most of the fields in thestruct tmare notlongbutintand printing them with%ldon a 64-bit machine leads to unpredictable behaviour. You could use%.2dor%02dto get your desired result (probably), though maybe you should use 4 instead of 2 for the year (though it does no damage with 2). On a 32-bit machine, you might get away with assizeof(int) == sizeof(long). Also, Win64 might be OK for the sam reason.
– Jonathan Leffler
Jan 2 at 19:48
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:28
@Fausto: the trouble with undefined behaviour is that the code is allowed to work as expected and to work other than as expected, and both are correct because the official requirement is undefined. One way that you can see it working on Machine A and failing on Machine B is if Machine A is 32-bit and Machine B is 64-bit. You could also run into issues if the working machine is Windows 64-bit and the non-working machine is not. And you could run into issues if the CPU on one machine is little-endian and on the other big-endian. You've not identified how similar your two machines are.
– Jonathan Leffler
Jan 4 at 8:41
add a comment |
arch2FILEpointer is not pointing to anyFILEobject.
– H.S.
Jan 2 at 19:40
1
You are using wrong format specifier infprintf(), which is undefined behavior.
– H.S.
Jan 2 at 19:42
Most of the fields in thestruct tmare notlongbutintand printing them with%ldon a 64-bit machine leads to unpredictable behaviour. You could use%.2dor%02dto get your desired result (probably), though maybe you should use 4 instead of 2 for the year (though it does no damage with 2). On a 32-bit machine, you might get away with assizeof(int) == sizeof(long). Also, Win64 might be OK for the sam reason.
– Jonathan Leffler
Jan 2 at 19:48
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:28
@Fausto: the trouble with undefined behaviour is that the code is allowed to work as expected and to work other than as expected, and both are correct because the official requirement is undefined. One way that you can see it working on Machine A and failing on Machine B is if Machine A is 32-bit and Machine B is 64-bit. You could also run into issues if the working machine is Windows 64-bit and the non-working machine is not. And you could run into issues if the CPU on one machine is little-endian and on the other big-endian. You've not identified how similar your two machines are.
– Jonathan Leffler
Jan 4 at 8:41
arch2 FILE pointer is not pointing to any FILE object.– H.S.
Jan 2 at 19:40
arch2 FILE pointer is not pointing to any FILE object.– H.S.
Jan 2 at 19:40
1
1
You are using wrong format specifier in
fprintf(), which is undefined behavior.– H.S.
Jan 2 at 19:42
You are using wrong format specifier in
fprintf(), which is undefined behavior.– H.S.
Jan 2 at 19:42
Most of the fields in the
struct tm are not long but int and printing them with %ld on a 64-bit machine leads to unpredictable behaviour. You could use %.2d or %02d to get your desired result (probably), though maybe you should use 4 instead of 2 for the year (though it does no damage with 2). On a 32-bit machine, you might get away with as sizeof(int) == sizeof(long). Also, Win64 might be OK for the sam reason.– Jonathan Leffler
Jan 2 at 19:48
Most of the fields in the
struct tm are not long but int and printing them with %ld on a 64-bit machine leads to unpredictable behaviour. You could use %.2d or %02d to get your desired result (probably), though maybe you should use 4 instead of 2 for the year (though it does no damage with 2). On a 32-bit machine, you might get away with as sizeof(int) == sizeof(long). Also, Win64 might be OK for the sam reason.– Jonathan Leffler
Jan 2 at 19:48
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with
%ld– Fausto
Jan 2 at 22:28
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with
%ld– Fausto
Jan 2 at 22:28
@Fausto: the trouble with undefined behaviour is that the code is allowed to work as expected and to work other than as expected, and both are correct because the official requirement is undefined. One way that you can see it working on Machine A and failing on Machine B is if Machine A is 32-bit and Machine B is 64-bit. You could also run into issues if the working machine is Windows 64-bit and the non-working machine is not. And you could run into issues if the CPU on one machine is little-endian and on the other big-endian. You've not identified how similar your two machines are.
– Jonathan Leffler
Jan 4 at 8:41
@Fausto: the trouble with undefined behaviour is that the code is allowed to work as expected and to work other than as expected, and both are correct because the official requirement is undefined. One way that you can see it working on Machine A and failing on Machine B is if Machine A is 32-bit and Machine B is 64-bit. You could also run into issues if the working machine is Windows 64-bit and the non-working machine is not. And you could run into issues if the CPU on one machine is little-endian and on the other big-endian. You've not identified how similar your two machines are.
– Jonathan Leffler
Jan 4 at 8:41
add a comment |
1 Answer
1
active
oldest
votes
3
From localtime:
Broken-down time is stored in the structure tm which is defined in <time.h> as follows:
struct tm {
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
All the tm structure member are of type int and you are using format specifier %ld for them in fprintf(). Instead, you should use %d format specifier.
From C Standard#7.21.6.1p9
9 If a conversion specification is invalid, the behavior is undefined.282) If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:50
@Fausto An undefined behavior includes it may execute incorrectly (either crashing or silently generating incorrect results), or it may fortuitously do exactly what the programmer intended. On my machine, with%ld, I was getting -03/01/2019, 01:4294967309:37result.
– H.S.
Jan 3 at 1:24
add a comment |
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1 Answer
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3
From localtime:
Broken-down time is stored in the structure tm which is defined in <time.h> as follows:
struct tm {
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
All the tm structure member are of type int and you are using format specifier %ld for them in fprintf(). Instead, you should use %d format specifier.
From C Standard#7.21.6.1p9
9 If a conversion specification is invalid, the behavior is undefined.282) If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:50
@Fausto An undefined behavior includes it may execute incorrectly (either crashing or silently generating incorrect results), or it may fortuitously do exactly what the programmer intended. On my machine, with%ld, I was getting -03/01/2019, 01:4294967309:37result.
– H.S.
Jan 3 at 1:24
add a comment |
3
From localtime:
Broken-down time is stored in the structure tm which is defined in <time.h> as follows:
struct tm {
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
All the tm structure member are of type int and you are using format specifier %ld for them in fprintf(). Instead, you should use %d format specifier.
From C Standard#7.21.6.1p9
9 If a conversion specification is invalid, the behavior is undefined.282) If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:50
@Fausto An undefined behavior includes it may execute incorrectly (either crashing or silently generating incorrect results), or it may fortuitously do exactly what the programmer intended. On my machine, with%ld, I was getting -03/01/2019, 01:4294967309:37result.
– H.S.
Jan 3 at 1:24
add a comment |
3
3
3
From localtime:
Broken-down time is stored in the structure tm which is defined in <time.h> as follows:
struct tm {
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
All the tm structure member are of type int and you are using format specifier %ld for them in fprintf(). Instead, you should use %d format specifier.
From C Standard#7.21.6.1p9
9 If a conversion specification is invalid, the behavior is undefined.282) If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
From localtime:
Broken-down time is stored in the structure tm which is defined in <time.h> as follows:
struct tm {
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
All the tm structure member are of type int and you are using format specifier %ld for them in fprintf(). Instead, you should use %d format specifier.
From C Standard#7.21.6.1p9
9 If a conversion specification is invalid, the behavior is undefined.282) If any argument is not the correct type for the corresponding conversion specification, the behavior is undefined.
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
answered Jan 2 at 19:49
H.S.H.S.
5,6291420
5,6291420
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:50
@Fausto An undefined behavior includes it may execute incorrectly (either crashing or silently generating incorrect results), or it may fortuitously do exactly what the programmer intended. On my machine, with%ld, I was getting -03/01/2019, 01:4294967309:37result.
– H.S.
Jan 3 at 1:24
add a comment |
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with%ld
– Fausto
Jan 2 at 22:50
@Fausto An undefined behavior includes it may execute incorrectly (either crashing or silently generating incorrect results), or it may fortuitously do exactly what the programmer intended. On my machine, with%ld, I was getting -03/01/2019, 01:4294967309:37result.
– H.S.
Jan 3 at 1:24
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with
%ld– Fausto
Jan 2 at 22:50
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with
%ld– Fausto
Jan 2 at 22:50
@Fausto An undefined behavior includes it may execute incorrectly (either crashing or silently generating incorrect results), or it may fortuitously do exactly what the programmer intended. On my machine, with
%ld, I was getting - 03/01/2019, 01:4294967309:37 result.– H.S.
Jan 3 at 1:24
@Fausto An undefined behavior includes it may execute incorrectly (either crashing or silently generating incorrect results), or it may fortuitously do exactly what the programmer intended. On my machine, with
%ld, I was getting - 03/01/2019, 01:4294967309:37 result.– H.S.
Jan 3 at 1:24
add a comment |
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arch2FILEpointer is not pointing to anyFILEobject.– H.S.
Jan 2 at 19:40
1
You are using wrong format specifier in
fprintf(), which is undefined behavior.– H.S.
Jan 2 at 19:42
Most of the fields in the
struct tmare notlongbutintand printing them with%ldon a 64-bit machine leads to unpredictable behaviour. You could use%.2dor%02dto get your desired result (probably), though maybe you should use 4 instead of 2 for the year (though it does no damage with 2). On a 32-bit machine, you might get away with assizeof(int) == sizeof(long). Also, Win64 might be OK for the sam reason.– Jonathan Leffler
Jan 2 at 19:48
Could that be the only reason? I'm trying to replicate that error in another machine but i can't. I'm running the same code and it prints the time the way it should be, even printing with
%ld– Fausto
Jan 2 at 22:28
@Fausto: the trouble with undefined behaviour is that the code is allowed to work as expected and to work other than as expected, and both are correct because the official requirement is undefined. One way that you can see it working on Machine A and failing on Machine B is if Machine A is 32-bit and Machine B is 64-bit. You could also run into issues if the working machine is Windows 64-bit and the non-working machine is not. And you could run into issues if the CPU on one machine is little-endian and on the other big-endian. You've not identified how similar your two machines are.
– Jonathan Leffler
Jan 4 at 8:41