为什么我们可以将整数分配给char变量

Question

I randomly surfed on StackOverflow. As I saw a question I became clueless. Why can we assign Integer values to a char variable?

Code snippet :

#include <stdio.h>
int main()
{
    char c = 130;
    unsigned char f = 130;

    printf("c = %d\nf = %d\n",c,f);
    return 0;
}

Output:

c = -126
f = 130

I always thought values have to be assigned to the right type indentifier, why can we do that?

Answer 1

That's because char is an integer type (the smallest one) and values of different integer types can be implicitly converted. But beware that your example code has implementation defined behavior on a typical machine with signed 8bit char *): 130 overflows (the maximum value would be 127 ) and the result of overflowing a signed integer type during conversion is implementation defined .

You might have asked this question because you thought char is for storing characters. This is actuall true, but characters are numbers. See Character Encoding for more details.

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*) whether char (without explicit signed or unsigned ) is signed is implementation-defined, as is the number of bits, but there must be at least 8.

Answer 2

Quoting C11 , chapter §6.5.16.1p2

In simple assignment (=), the value of the right operand is converted to the type of the assignment expression and replaces the value stored in the object designated by the left operand.

This implies that the RHS in an assignment operator is implicitly converted to the type of the variable on the LHS. In your case, the integer constant is converted to char type.

Also, there is no char constant in C. The character constants like 'a' , 'B' are all of int type.