PrintFormat and StringFormat with variable precision

[Gustavo Hennemann]

Hello folks,

According to C and C++ definitions, is possible to use printf with variables "width" and "precision".

In MQL documentation is clear that we can use variable "width", but is not clear to "precision". Is possible to use variable "precision"? Is there any way to do this?

https://www.mql5.com/en/docs/common/printformat

I'm using this code to test. Also, the variable "width" doesn't have the same behavior as the static one, see "strValue1" and "strValue3, is not possible to put the zeroes.

   string strValue1 = StringFormat("Format test: %07.3f", 1.25);        // Result --> Format test: 001.250
   string strValue2 = StringFormat("Format test: %*.3f", 7, 1.25);      // Result --> Format test:   1.250
   string strValue3 = StringFormat("Format test: %*.3f", 07, 1.25);     // Result --> Format test:   1.250
   string strValue4 = StringFormat("Format test: %*.*f", 07, 3, 1.25);  // Result --> Format test:  *.*f

[Carl Schreiber]

you can do it this way (it's even shown in the help, F1):

double val = 1.7612345679; // price
string fmt = StringFormat( "%%0%d.%df", 3+_Digits, _Digits ), // => "%08.5"
       var = StringFormat(fmt,val);
=> 01.7612

You can put it even into a function:

string sPrintf(double val, int zeros, int digs) { string _=StringFormat("%%0%d.%df", zeros+1+digs, digs); return(StringFormat(_,val)); }

(untested!)

[Gustavo Hennemann]

Carl Schreiber:

you can do it this way (it's even shown in the help, F1):

You can put it even into a function:

(untested!)

Thanks @Carl Schreiber, your code works well, but it is not very practical if we use a more long expression. So, I tried compress all the code and I got:

{
   double A = 1.25;
   double B = 3.45;
   double C = 5.01;
   int    z = 7;
   int    d = 3;
   
   // In MQL5 and Standard C (static precision):
   string strValue5 = StringFormat("A: %7.3f, B: %7.3f, C: %7.3f", A, B, C);  // Result --> A:   1.250, B:   3.450, C:   5.010
   
   // In Standard C (variable precision):
   string strValue6 = StringFormat("A: %*.*f, B: %*.*f, C: %*.*f", z, d, A, z, d, B, z, d, C);  // Result --> A:  *.*f, B:  *.*f, C:  *.*f
   
   // In MQL5 (variable precision):
   string strValue7 = StringFormat("A: %s, B: %s, C: %s", prt(A, z, d) , prt(B, z, d), prt(C, z, d));  // Result --> A: 0000001.250, B: 0000003.450, C: 0000005.010
}

...

string prt(double val, int zeros, int digs)
{
   string _=StringFormat("%%0%d.%df", zeros+1+digs, digs);
   return(StringFormat(_,val));
}

Working very well, thanks!