C++ compare to string dates

问题

I need to compare 2 string dates to see if one date is later then another. The date format for both dates is at the bottom. i can rearrange this for what ever is easiest. I have boost but it doesn't have to be, ive been through so many examples and can't seem to wrap my brain around getting it to work. Thanks in advance basically i want

2012-12-06 14:28:51

if (date1 < date2) {
 // do this
}
else {
 // do that
}

回答1:

It looks like the date format your using is already in lexicographical order and a standard string comparison will work, something like:

std::string date1 = "2012-12-06 14:28:51";
std::string date2 = "2012-12-06 14:28:52";
if (date1 < date2) {
    // ...
}
else {
    // ...
}

You will need to make sure that spacing and punctuation is consistent when using this format, in particular something like 2012-12-06 9:28:51 will break the comparison. 2012-12-06 09:28:51 will work though.

回答2:

You're lucky - your dates are already in the proper format to do a standard string comparison and get the correct results. All the parts go from most significant to least significant, and you're using 24-hour times.

If these are std::strings you can use the < just as you have in your sample. If they're C-style character array strings, use strcmp.

回答3:

strcmp() returns an integral value indicating the relationship between the strings:

 result = strcmp( string1, string2 ); 
 if( result > 0 )  strcpy( tmp, "greater than" );
 else if( result < 0 )  strcpy( tmp, "less than" );

A zero value indicates that both strings are equal. A value greater than zero indicates that the first character that does not match has a greater value in str1 than in str2; And a value less than zero indicates the opposite.

#include <string.h>
#include <stdio.h>

char string1[] = "2012-12-06 14:28:51";
char string2[] = "2011-12-06 14:28:51";

int main( void )
{
   char tmp[20];
   int result;

   printf( "Compare strings:\n   %s\n   %s\n\n\n", string1, string2 );
   result = strcmp( string1, string2 );

   if( result > 0 )        strcpy( tmp, "greater than" );
   else if( result < 0 )   strcpy( tmp, "less than" );
   else    strcpy( tmp, "equal to" );

   printf( "   strcmp:   String 1 is %s string 2\n\n", tmp );

   return 0;
}

来源：https://stackoverflow.com/questions/8406703/c-compare-to-string-dates

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c++

datetime

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