String Format alternative in C

Question

I don t have much experience working with C    Rather I have worked more in C  and so  I wanted to ask my question by relating to what I would have done in there  I have to generate a specific format of the string  which I have to pass to another function  In C   I would have easily generated the string through the below simple code   string a    test   string b    text txt   string c    text1 txt    String Format   0   1   gt   2    a  b  c     By generating such an above string  I should be able to pass this in system    However  system only accepts char   I am on Win32 C    not C   CLI   and cannot use boost since it would include too much inclusion of all the files for a project which itself is very small  Something like sprintf   looks useful to me  but sprintf does not accept string as the a  b and c parameters  Any suggestions how I can generate these formatted strings to pass to system in my program

User · Answer

In addition to options suggested by others I can recommend the fmt library which implements string formatting similar to str.format in Python and String.Format in C#. Here's an example:

std::string a = "test";
std::string b = "text.txt";
std::string c = "text1.txt";
std::string result = fmt::format("{0} {1} > {2}", a, b, c);

Disclaimer: I'm the author of this library.

User · Answer

You can just concatenate the strings and build a command line   std  string command   a         b      gt      c  system command c str       You don t need any extra libraries for this

User · Answer

The C   way would be to use a std  stringstream object as   std  stringstream fmt  fmt  lt  lt  a  lt  lt       lt  lt  b  lt  lt     gt     lt  lt  c    The C way would be to use sprintf    The C way is difficult to get right since    It is type unsafe Requires buffer management    Of course  you may want to fall back on the C way if performance is an issue  imagine you are creating fixed-size million little stringstream objects and then throwing them away

User · Answer

For completeness  the boost way would be to use boost  format  cout  lt  lt  boost  format   s  s  gt   s     a   b   c    Take your pick  The boost solution has the advantage of type safety with the sprintf format  for those who find the  lt  lt  syntax a bit clunky

User · Answer

For the sake of completeness  you may use std  stringstream    include  lt iostream gt   include  lt sstream gt   include  lt string gt   int main         std  string a    a   b    b   c    c          apply formatting     std  stringstream s      s  lt  lt  a  lt  lt       lt  lt  b  lt  lt     gt     lt  lt  c         assign to std  string     std  string str   s str        std  cout  lt  lt  str  lt  lt    n         Or  in this case  std  string s very own string concatenation capabilities    include  lt iostream gt   include  lt string gt   int main         std  string a    a   b    b   c    c       std  string str   a         b      gt      c      std  cout  lt  lt  str  lt  lt    n       For reference    http   en cppreference com w cpp string basic string operator      If you really want to go the C way  Here you are    include  lt iostream gt   include  lt string gt   include  lt vector gt   include  lt cstdio gt   int main         std  string a    a   b    b   c    c       const char fmt       s  s  gt   s          use std  vector for memory management  to avoid memory leaks      std  vector lt char gt   size type size   256      std  vector lt char gt  buf      do              use snprintf instead of sprintf  to avoid buffer overflows             snprintf returns the required size  without terminating null             if buffer is too small initially  loop should run at most twice         buf resize size 1           size   std  snprintf                   amp buf 0   buf size                    fmt  a c str    b c str    c c str           while  size 1  gt  buf size            assign to std  string     std  string str buf begin    buf begin   size       std  cout  lt  lt  str  lt  lt    n       For reference    http   en cppreference com w cpp io c fprintf     Then  there s the Boost Format Library  For the sake of your example    include  lt iostream gt   include  lt string gt   include  lt boost format hpp gt   int main         std  string a    a   b    b   c    c          apply format     boost  format fmt   boost  format   s  s  gt   s     a   b   c          assign to std  string     std  string str   fmt str        std  cout  lt  lt  str  lt  lt    n

User · Answer

You can use sprintf in combination with std  string c str     c str   returns a const char  and works with sprintf   string a    test   string b    text txt   string c    text1 txt   char  x   new char a length     b length     c length     32    sprintf x    s  s  gt   s   a c str    b c str    c c str       string str   x  delete   x    or you can use a pre-allocated char array if you know the size   string a    test   string b    text txt   string c    text1 txt   char x 256    sprintf x    s  s  gt   s   a c str    b c str    c c str

User · Answer

As already mentioned the C   way is using stringstreams    include  lt sstream gt   string a    test   string b    text txt   string c    text1 txt    std  stringstream ostr  ostr  lt  lt  a  lt  lt       lt  lt  b  lt  lt     gt     lt  lt  c    Note that you can get the C string from the string stream object like so   std  string formatted string   ostr str    const char  c str   formatted string c str

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