Why use String Format

Question

Why would anyone use String Format in C  and VB  NET as opposed to the concatenation operators   amp  in VB  and   in C     What is the main difference  Why are everyone so interested in using String Format  I am very curious

User · Accepted Answer

I can see a number of reasons   Readability  string s   string Format  Hey   0  it is the  1 st day of  2    I feel  3      name   day   month   feeling     vs   string s    Hey      name     it is the      day    st day of      month       I feel     feeling          Format Specifiers  and this includes the fact you can write custom formatters   string s   string Format  Invoice number   0 0000     invoiceNum     vs   string s    Invoice Number         0000     invoiceNum  Substr         can t even be bothered to type it      String Template Persistence  What if I want to store string templates in the database   With string formatting    id          translation   1         Welcome  0  to  1    Today is  2     2         You have  0  products in your basket    3         Thank-you for your order   Your  0  will arrive in  1  working days    vs    id          translation   1         Welcome   2         to   3            Today is   4              5         You have   6         products in your basket    7         Someone   8         just shoot   9         the developer

User · Answer

Several reasons    String Format   is very powerful  You can use simple format indicators  like fixed width  currency  character lengths  etc  right in the format string  You can even create your own format providers for things like expanding enums  mapping specific inputs to much more complicated outputs  or localization  You can do some powerful things by putting format strings in configuration files  String Format   is often faster  as it uses a StringBuilder and an efficient state machine behind the scenes  whereas string concatenation in  Net is relatively slow  For small strings the difference is negligible  but it can be noticable as the size of the string and number of substituted values increases  String Format   is actually more familiar to many programmers  especially those coming from backgrounds that use variants of the old C printf   function    Finally  don t forget StringBuilder AppendFormat     String Format   actually uses this method behind the scenes   and going to the StringBuilder directly can give you a kind of hybrid approach  explicitly use  Append    analogous to concatenation  for some parts of a large string  and use  AppendFormat   in others        edit  Original answer is now 8 years old  and I ve since seen an indication this may have changed when string interpolation was added to  Net  However  I haven t gone back to the reference source to verify the change yet

User · Answer

One reason it is not preferable to write the string like  string   Value   string  is because of Localization  In cases where localization is occurring we want the localized string to be correctly formatted  which could be very different from the language being coded in    For example we need to show the following error in different languages   MessageBox Show String Format ErrorManager GetError  PIDV001   Description  proposalvalue ProposalSource    where    ErrorCollector GetError  ERR001   ErrorDescription  returns a string like  Your ID  0  is not valid   This message must be localized in many languages  In that case we can t use   in C   We need to follow string format

User · Answer

String Format adds many options in addition to the concatenation operators  including the ability to specify the specific format of each item added into the string   For details on what is possible  I d recommend reading the section on MSDN titled Composite Formatting   It explains the advantage of String Format  as well as xxx WriteLine and other methods that support composite formatting  over normal concatenation operators

User · Answer

Besides being a bit easier to read and adding a few more operators  it s also beneficial if your application is internationalized   A lot of times the variables are numbers or key words which will be in a different order for different languages   By using String Format  your code can remain unchanged while different strings will go into resource files   So  the code would end up being  String Format resource GetString  MyResourceString    str1  str2  str3     While your resource strings end up being   English    blah blah  0  blah blah  1  blah  2    Russian     0  blet blet blet  2  blet  1    Where Russian may have different rules on how things get addressed so the order is different or sentence structure is different

User · Answer

First  I find  string s   String Format       Your order  0  will be delivered on  1 yyyy-MM-dd   Your total cost is  2 C         orderNumber      orderDeliveryDate      orderCost      far easier to read  write and maintain than  string s    Your order                orderNumber ToString                  will be delivered on                orderDeliveryDate ToString  yyyy-MM-dd                                  Your total cost is                orderCost ToString  C                        Look how much more maintainable the following is  string s   String Format       Year    0 yyyy   Month    0 MM   Day    0 dd        date      over the alternative where you d have to repeat date three times   Second  the format specifiers that String Format provides give you great flexibility over the output of the string in a way that is easier to read  write and maintain than just using plain old concatenation  Additionally  it s easier to get culture concerns right with String Format   Third  when performance does matter  String Format will outperform concatenation  Behind the scenes it uses a StringBuilder and avoids the Schlemiel the Painter problem

User · Answer

There s interesting stuff on the performance aspects in this question  However I personally would still recommend string Format unless performance is critical for readability reasons   string Format   0    1    key  value     Is more readable than  key          value   For instance  Also provides a nice separation of concerns  Means you can have  string Format GetConfigValue  KeyValueFormat    key  value     And then changing your key value format from   0    1   to   0  -  1   becomes a config change rather than a code change   string Format also has a bunch of format provision built into it  integers  date formatting  etc

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