MQL4 Reference Common Functions Print


It enters a message in the Expert Advisor log. Parameters can be of any type.

void  Print(
   argument,     // first value
   ...           // next values



[in]  Any values separated by commas. The number of parameters cannot exceed 64.


Arrays cannot be passed to the Print() function. Arrays must be input element-by-element.

Data of double type are shown with the accuracy of up to  16 digits after a decimal point, and can be output either in traditional or in scientific format, depending on what entry will be more compact. Data of float type are output with 5 digits after a decimal point. To output real numbers with another accuracy or in a predefined format, use the PrintFormat() function.

Data of bool type are output as "true" or "false" lines. Dates are shown as YYYY.MM.DD HH:MI:SS. To show data in another format, use TimeToString(). Data of color type are returned either as R,G,B line or as a color name, if this color is present in the color set.

Print() function does not work during optimization in the Strategy Tester.


void OnStart()
//--- Output DBL_MAX using Print(), this is equivalent to PrintFormat(%%.16G,DBL_MAX)
   Print("---- how DBL_MAX looks like -----");
//--- Now output a DBL_MAX number using PrintFormat()
//--- Output to the Experts journal
// Print(DBL_MAX)=1.797693134862316e+308
// PrintFormat(%.16G,DBL_MAX)=1.797693134862316E+308
//--- See how float is output
   float c=(float)M_PI// We should explicitly cast to the target type
   Print("c=",c, "    Pi=",M_PI"    (float)M_PI=",(float)M_PI);
// c=3.14159    Pi=3.141592653589793    (float)M_PI=3.14159
//--- Show what can happen with arithmetic operations with real types
   double a=7,b=200;
   Print("---- Before arithmetic operations");
   Print("a=",a,"   b=",b);
//--- Divide a by b (7/200)
//--- Now emulate restoring a value in the b variable
   b=7.0/a; // It is expected that b=7.0/(7.0/200.0)=>7.0/7.0*200.0=200 - but it differs
//--- Output the newly calculated value of b
   Print("----- After arithmetic operations");
//--- Output to the Experts journal
// Print(b)=200.0
// Print(DoubleToString(b,16))=199.9999999999999716 (see that b is no more equal to 200.0)   
//--- Create a very small value epsilon=1E-013
   double epsilon=1e-13;
   Print("---- Create a very small value");
   Print("epsilon=",epsilon); // Get epsilon=1E-013
//--- Now subtract epsilon from b and again output the value to the Experts journal
//--- Use two ways
   Print("---- After subtracting epsilon from the b variable");
//--- Output to the Experts journal
// Print(b)=199.9999999999999  (now the value of b after subtracting epsilon cannot be rounded to 200)
// Print(DoubleToString(b,16))=199.9999999999998578
//    (now the value of b after subtracting epsilon cannot be rounded to 200)

See also

Alert(), Comment(), DoubleToString(), StringFormat()