char类型的两个数经过异或运算之后数据类型怎么变成int类型了？

Question

#include
int main(void)
{
char a = 0xa2;
char b = 0x32;
char test = a ^ b;
printf("%#x", test);

 return 0;

}

我期望的打印结果是：0x90
结果打印的是：0xffffff90 好像数据变成int类型了，这个是怎么回事？

Answer 1

c
int or wint_t
When used with printf functions, specifies a single-byte character; when used with wprintf functions, specifies a wide character.

C
int or wint_t
When used with printf functions, specifies a wide character; when used with wprintf functions, specifies a single-byte character.

d
int
Signed decimal integer.

i
int
Signed decimal integer.

o
int
Unsigned octal integer.

u
int
Unsigned decimal integer.

x
int
Unsigned hexadecimal integer, using "abcdef."

X
int
Unsigned hexadecimal integer, using "ABCDEF."

e
double
Signed value having the form [ – ]d.dddd e [sign]dd[d] where d is a single decimal digit, dddd is one or more decimal digits, dd[d] is two or three decimal digits depending on the output format and size of the exponent, and sign is + or –.

E
double
Identical to the e format except that E rather than e introduces the exponent.

f
double
Signed value having the form [ – ]dddd.dddd, where dddd is one or more decimal digits. The number of digits before the decimal point depends on the magnitude of the number, and the number of digits after the decimal point depends on the requested precision.

g
double
Signed value printed in f or e format, whichever is more compact for the given value and precision. The e format is used only when the exponent of the value is less than –4 or greater than or equal to the precision argument. Trailing zeros are truncated, and the decimal point appears only if one or more digits follow it.

G
double
Identical to the g format, except that E, rather than e, introduces the exponent (where appropriate).

a
double
Signed hexadecimal double precision floating point value having the form [−]0xh.hhhh p±dd, where h.hhhh are the hex digits (using lower case letters) of the mantissa, and dd are one or more digits for the exponent. The precision specifies the number of digits after the point.

A
double
Signed hexadecimal double precision floating point value having the form [−]0Xh.hhhh P±dd, where h.hhhh are the hex digits (using capital letters) of the mantissa, and dd are one or more digits for the exponent. The precision specifies the number of digits after the point.

n
Pointer to integer
Number of characters successfully written so far to the stream or buffer; this value is stored in the integer whose address is given as the argument. See Security Note below.

p
Pointer to void
Prints the argument as an address in hexadecimal digits.

s
String
When used with printf functions, specifies a single-byte–character string; when used with wprintf functions, specifies a wide-character string. Characters are printed up to the first null character or until the precision value is reached.

S
String
When used with printf functions, specifies a wide-character string; when used with wprintf functions, specifies a single-byte–character string. Characters are printed up to the first null character or until the precision value is reached.