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C conversion specifiers and modifiers

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A handy reference to C conversion specifiers and modifiers

In this post I want to create a helpful reference for all the C conversion specifiers you can use, commonly with printf(), scanf() and similar I/O functions.

%d / %iSigned decimal integer
%uUnsigned decimal integer
%cUnsigned char
%pPointer in hexadecimal form
%oUnsigned octal integer
%x / %XUnsigned hexadecimal number
%eFloating point number in exponential format in e notation
%EFloating point number in exponential format in E notation
%fdouble number in decimal format
%g / %Gdouble number in decimal format or exponential format depending on the value

In addition to those specifiers, we have a set of modifiers.

Let’s start with digits. Using a digit between % and the format specifier, you can tell the minimum field width. Example: %3d will take 3 spaces regardless of the number printed.


printf("%4d\n", 1);
printf("%4d\n", 12);
printf("%4d\n", 123);
printf("%4d\n", 1234);

should print


If you put a dot before the digit, you are not telling the precision: the number of decimal digits. This of course applies to decimal numbers. Example:

printf("%4.2f\n", 1.0);
printf("%4.3e\n", 12.232432442);
printf("%4.1e\n", 12.232432442);
printf("%4.1f\n", 123.22);

will print:


In addition to digits, we have 3 special letters: h, l and L.

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