c++ - uint8_t can't be printed with cout

Question

I have a weird problem about working with integers in C++.

I wrote a simple program that sets a value to a variable and then prints it, but it is not working as expected.

My program has only two lines of code:

uint8_t aa = 5;

cout << "value is " << aa << endl;

The output of this program is value is

I.e., it prints blank for aa.

When I change uint8_t to uint16_t the above code works like a charm.

I use Ubuntu 12.04 (Precise Pangolin), 64-bit, and my compiler version is:

gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)

Answer 1

It doesn't really print a blank, but most probably the ASCII character with value 5, which is non-printable (or invisible). There's a number of invisible ASCII character codes, most of them below value 32, which is the blank actually.

You have to convert aa to unsigned int to output the numeric value, since ostream& operator<<(ostream&, unsigned char) tries to output the visible character value.

uint8_t aa=5;

cout << "value is " << unsigned(aa) << endl;