How to calculate the difference in months between two dates in C? Is there is equivalent of VB's DateDiff method in C. I need to find difference in months between two dates that are years apart. I don't want to divide this number by 30 because not every month is 30 days and since the two operand values are quite apart from each other, I am afraid dividing by 30 might give me a wrong value. Assuming the day of the month is irrelevant i. Month Or, assuming you want an approximate number of 'average months' between the two dates, the following should work for all but very huge date differences. Update with thanks to If using the 'average months' method, a slightly more accurate number to use for the 'average number of days per year' is. DrunkCoder it depends on the requirements of a given system. In some cases your solution may indeed be the best choice. If the results of your formula deliver what the system requires then it's clearly the right choice. If not, then something else is required. Some calculations were divide by number of days, round up by 30 to get monthly figure. Sometimes counting months assumed every date starts on the first of the month, count whole months accordingly. There is no best method when it comes to calculating dates. Unless you are the customer you're writing code for, push this back up the chain and get it clarified, possibly by you customers accountant. CompareDates compareTo, now ; Console. Milliseconds ; } Outputs: Years: 1 Months: 5 Days: 27 Hours: 1 Minutes: 36 Seconds: 50 Milliseconds: 0 For convenience, I've lumped the logic into the DateTimeSpan struct, but you may move the method CompareDates wherever you see fit. Also note, it doesn't matter which date comes before the other. AddYears years ; } else years++; break; case Phase. AddMonths months ; if current. Done; } else days++; break; } } return span; } } Deeptechtons, nice catch. Right now the result is 1 month. Month - 1 - from. Month - 1 ; if from. In this case from December 31st 2015, until June 30 2016, 6 complete months will have passed since June has 30 days but your code would return 5. NET via MSDN and it seems that it has a lot of usages. There is no such a built-in method in C. Even it's not a good idea you can call VB's in C. DateDiff in your code Why do you think it's not a good idea? Intuitively, I would guess that the library is 'just another. NET library' to the runtime. Note, I am playing devil's advocate here, I would also be relunctant to do this since it just 'feels wrong' kind of cheating but I wonder if there is any convincing technical reason not to do this. Those libraries are implemented in 100% managed code, so it's all the same as everything else. The only conceivable difference is that the Microsoft. There's no reason to cheat yourself out of thoroughly tested and useful features just because you've chosen to write your program in C. This goes for things like My. Or are you saying that purely hypothetically? And yeah, it might mess with the minds of some of your C buddies who have been writing an epic amount of code to do something that you can do in one line with the right using statement, but I doubt there'll be any serious damage. It's the extra code 'noise' introduced by calling such an unusual from a C POV method that I'd be keen to avoid. In a well organised team such things would anyway be picked up in code review and can be easily avoided. I described such methods as 'strange' only because, from a. NET POV, there's no reason for DateAndTime. Year to exist, given that DateTime has a Year property. It only exists to make VB. NET appear more like VB6. As a former VB6 programmer, I can appreciate this ;- — Jan 10 '11 at 10:34 I just needed something simple to cater for e. The day of month didn't matter in my case because it always happens to be the last day of the month. Month + 12 - d2. GetMonthDays; } Here is a simple solution that works at least for me. Month ; return retVal; } You can have a function something like this. Month ; if endDate. DiffYears d1, d2 ; Here's a much more concise solution using VB. Net DateDiff for Year, Month, Day only. You can load the DateDiff library in C as well. Year, date1, date2 - date1. AddYears 5 ; You can create another method called DiffYears and apply exactly the same logic as above and AddYears instead of AddMonths in the while loop. This is in response to Kirk Woll's answer. I don't have enough reputation points to reply to a comment yet... I liked Kirk's solution and was going to shamelessly rip it off and use it in my code, but when I looked through it I realized it's way too complicated. Unnecessary switching and looping, and a public constructor that is pointless to use. Milliseconds ; } In my case it is required to calculate the complete month from the start date to the day prior to this day in the next month or from start to end of month. There's 3 cases: same year, previous year and other years. If the day of the month does not matter... Year + 12 - start. Month; } } I wrote a function to accomplish this, because the others ways weren't working for me. ToString ; } My understanding of the total months difference between 2 dates has an integral and a fractional part the date matters. The integral part is the full months difference. The fractional part, for me, is the difference of the % of the day to the full days of month between the starting and ending months. Month -1 - double from. This solution calculates between two dates the months between assuming you want to save the day of month for comparison, meaning that the day of the month is considered in the calculation Example, if you have a date of 30 Jan 2012, 29 Feb 2012 will not be a month but 01 March 2013 will. Here is the answer to the above 2 comments - The number of months between 1-may-2010 and 16-jun-2010 is 1 month, the number of months between 31-dec-2010 and 1-jan-2011 is 0. It would be very foolish to calculate them as 1. People who have worked on credit card, mortgage processing, tax processing, rent processing, monthly interest calculations and a vast variety of other business solutions would agree. Problem is that such a function is not included in C or VB. NET for that matter. Datediff only takes into account years or the month component, so is actually useless. Here are some real-life examples of where you need to and correctly can calculate months: You lived in a short-term rental from 18-feb to 23-aug. How many months did you stay there? The answer is a simple - 6 months You have a bank acount where interest is calculated and paid at the end of every month. You deposit money on 10-jun and take it out 29-oct same year. How many months do you get interest for? This is one of the reasons why accounting is not mathematics. In accounting the result depends on the way you calculate it.. Were the dates exlusive or inclusive? Did you ask for number of months crossed, touched, or passed? Did you want round-up, round-down, or exact? Accountants are more likely to agree, because at some point they will use maths to check with what options they might accidentially sum up the same period twice, etc. Even your examples of calculations are disputable and region-dependent, or plainly invalid as they assume extra business rules like ignoring extra days. AddYears years ; } else years++; break; case Phase. AddMonths months ; } else months++; break; case Phase. Done; } else days++; break; } } return span; } }.
