The use of PHP's sprintf function control floating-point number format _php instance

Control floating-point printing format

The printing and formatting control of floating point numbers is a common function of sprintf, floating-point numbers use the format character "%f" control, the default is to retain 6 digits after the decimal, such as:

Copy Code code as follows:

sprintf ("%f", 3.1415926); Result: "3.141593"

However, sometimes we want to control the width and scale of the print, and then we should use the "%M.NF" format where m represents the overall width of the printed number, and n represents the number of digits after the decimal point. Like what:

Copy Code code as follows:

sprintf ("%9.3f", 3.1415926); Right alignment: The number of digits is not enough to complete with spaces. Result: "3.142"
sprintf ("%-9.3f", 3.1415926); Left-aligned: the number of digits is not enough to complete with spaces. Result: "3.142"
sprintf ("%.3f", 3.1415926); Do not specify total width, result: "3.142"

Pay attention to a problem

Copy Code code as follows:

$num = 100;
sprintf ("%.2f", $num);
sprintf ("%.2f", (double) $num);

Are the two results really the same? Although it looks the same, the following reasons may be instructive.
The reason for this is that the caller does not know that the format control character corresponding to Num is a "%f" when the parameter presses the stack. The function is not aware of the execution of the stack is a whole number of times, so the poor save the integer $num of the 4 bytes were use robust reporting forced as a floating-point format to explain the whole mess.