Difference between signed unsigned char

Question

So I know that the difference between a signed int and unsigned int is that a bit is used to signify if the number if positive or negative  but how does this apply to a char  How can a character be positive or negative

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A signed char is a signed value which is typically smaller than  and is guaranteed not to be bigger than  a short   An unsigned char is an unsigned value which is typically smaller than  and is guaranteed not to be bigger than  a short   A type char without a signed or unsigned qualifier may behave as either a signed or unsigned char  this is usually implementation-defined  but there are a couple of cases where it is not   If  in the target platform s character set  any of the characters required by standard C would map to a code higher than the maximum  signed char   then  char  must be unsigned  If  char  and  short  are the same size  then  char  must be signed   Part of the reason there are two dialects of  C   those where char is signed  and those where it is unsigned  is that there are some implementations where char must be unsigned  and others where it must be signed

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I slightly disagree with the above  The unsigned char simply means  Use the most significant bit instead of treating it as a bit flag for   - sign when performing arithmetic operations   It makes significance if you use char as a number for instance    typedef char BYTE1  typedef unsigned char BYTE2   BYTE1 a  BYTE2 b    For variable a  only 7 bits are available and its range is  -127 to 127        - 2 7 -1  For variable b all 8 bits are available and the range is 0 to 255  2 8 -1    If you use char as character   unsigned  is completely ignored by the compiler just as comments are removed from your program

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This because a char is stored at all effects as a 8-bit number  Speaking about a negative or positive char doesn t make sense if you consider it an ASCII code  which can be just signed    but makes sense if you use that char to store a number  which could be in range 0-255 or in -128  127 according to the 2-complement representation      it can be also unsigned  it actually depends on the implementation I think  in that case you will have access to extended ASCII charset provided by the encoding used

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Representation is the same  the meaning is different  e g  0xFF  it both represented as  FF   When it is treated as  char   it is negative number -1  but it is 255 as unsigned  When it comes to bit shifting  it is a big difference since the sign bit is not shifted  e g  if you shift 255 right 1 bit  it will get 127  shifting  -1  right will be no effect

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The same way how an int can be positive or negative  There is no difference  Actually on many platforms unqualified char is signed

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There are three char types   plain  char  signed char and unsigned char   Any char is usually an 8-bit integer  and in that sense  a signed and unsigned char have a useful meaning  generally equivalent to uint8 t and int8 t    When used as a character in the sense of text  use a char  also referred to as a plain char    This is typically a signed char but can be implemented either way by the compiler     Technically  a char can be any size as long as sizeof char  is 1  but it is usually an 8-bit integer

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There s no dedicated  character type  in C language  char is an integer type  same  in that regard  as int  short and other integer types  char just happens to be the smallest integer type  So  just like any other integer type  it can be signed or unsigned   It is true that  as the name suggests  char is mostly intended to be used to represent characters  But characters in C are represented by their integer  codes   so there s nothing unusual in the fact that an integer type char is used to serve that purpose   The only general difference between char and other integer types is that plain char is not synonymous with signed char  while with other integer types the signed modifier is optional implied

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The same way -- e g  if you have an 8-bit char  7 bits can be used for magnitude and 1 for sign  So an unsigned char might range from 0 to 255  whilst a signed char might range from -128 to 127  for example

[c] Difference between signed / unsigned char

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