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cimplicit-conversioninteger-promotion

Size of unsigned char is 8 bits but why can I shift it (left or right) by or upto 31 bits?

So here is my code 

#include <stdio.h>                  
int main(void) {
    unsigned char ch = 244;      
    ch = ch << 31;                   
    return 0;
}

I can shift ch upto 31 bits that's means ch is of 32 bits but how ? sizeof(ch) is also 1 byte only.

Solution

  • [...] that means ch is of 32 bits [...] ?

    It isn't. The result of the shift, which is of type int, is truncated to 8 bits when assigned back to ch.

    You can verify this by examining the value of ch.

    gcc spots this if -Wconversion is turned on:

    $ gcc -Wconversion test.c
test.c:4:13: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wconversion]
    ch = ch << 31;
       ~ ~~~^~~~~
1 warning generated.