Ambiguous overload call to abs double

Question

I have the following C   code    include  lt math h gt   include  lt cmath h gt          per http   www cplusplus com reference clibrary cmath abs      snip      if    loan balance  lt  0   amp  amp   abs loan balance   gt  loan payment                  and make blows up on   error  call of overloaded  abs double   is ambiguous   also of interest    usr include stdlib h 785  note  candidates are  int abs int    How can I specify that the compiler needs to call the abs   in cmath h that can handle floats   Compiler info  Not sure if this matters     some man some box   some code    gcc -v Using built-in specs  Target  i386-redhat-linux Configured with     configure --prefix  usr --mandir  usr share man --infodir  usr     share info --enable-shared --enable-threads posix --enable-checking release --with-system-zlib --enable-  cxa atexit --disable-libunwind-exceptions --enable-libgcj-multifile --enable-languages c c   objc obj-c   java fortran ada --enable-java-awt gtk --disable-dssi --enable-plugin --with-java-home  usr lib jvm java-1 4 2-gcj-1 4 2 0 jre --with-cpu generic --host i386-redhat-linux Thread model  posix gcc version 4 1 2 20080704  Red Hat 4 1 2-44

User · Answer

Use fabs   instead of abs    it s the same but for floats instead of integers

User · Answer

The header  lt math h gt  is a C std lib header  It defines a lot of stuff in the global namespace  The header  lt cmath gt  is the C   version of that header  It defines essentially the same stuff in namespace std   There are some differences  like that the C   version comes with overloads of some functions  but that doesn t matter   The header  lt cmath h gt  doesn t exist    Since vendors don t want to maintain two versions of what is essentially the same header  they came up with different possibilities to have only one of them behind the scenes  Often  that s the C header  since a C   compiler is able to parse that  while the opposite won t work   and the C   header just includes that and pulls everything into namespace std  Or there s some macro magic for parsing the same header with or without namespace std wrapped around it or not  To this add that in some environments it s awkward if headers don t have a file extension  like editors failing to highlight the code etc    So some vendors would have  lt cmath gt  be a one-liner including some other header with a  h extension  Or some would map all includes matching  lt cblah gt  to  lt blah h gt   which  through macro magic  becomes the C   header when   cplusplus is defined  and otherwise becomes the C header  or  lt cblah h gt  or whatever    That s the reason why on some platforms including things like  lt cmath h gt   which ought not to exist  will initially succeed  although it might make the compiler fail spectacularly later on    I have no idea which std lib implementation you use  I suppose it s the one that comes with GCC  but this I don t know  so I cannot explain exactly what happened in your case  But it s certainly a mix of one of the above vendor-specific hacks and you including a header you ought not to have included yourself  Maybe it s the one where  lt cmath gt  maps to  lt cmath h gt  with a specific  set of  macro s  which you hadn t defined  so that you ended up with both definitions    Note  however  that this code still ought not to compile     include  lt cmath gt   double f double d      return abs d       There shouldn t be an abs   in the global namespace  it s std  abs     However  as per the above described implementation tricks  there might well be  Porting such code later  or just trying to compile it with your vendor s next version which doesn t allow this  can be very tedious  so you should keep an eye on this

User · Answer

Its boils down to this  math h is from C and was created over 10 years ago  In math h  due to its primitive nature  the abs   function is  essentially  just for integer types and if you wanted to get the absolute value of a double  you had to use fabs     When C   was created it took math h and made it cmath  cmath is essentially math h but improved for C    It improved things like having to distinguish between fabs   and abs  and just made abs   for both doubles and integer types  In summary either  Use  math h and use abs   for integers  fabs   for doubles or use cmath and just have abs for everything  easier and recommended   Hope this helps anyone who is having the same problem

User · Answer

In my cases  I solved the problem when using the labs   instead of abs

[c++] Ambiguous overload call to abs(double)

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