将字符类型转换为整数类型是否安全？

Question

int main() {
    char ch = 'a';
    int x;
    x = ch; 
    printf("x=%c", x);
}

Is this code safe to use (considering endiness of machine)?

Answer 1

Yes, it is safe to cast a character (like char ) type to an integer type (like int ).

In this answer and others, endian-ness is not a factor.

There are 4 conversions going on here and no casting:

1. a is character of the C encoding. 'a' converts to an int at compile time.

    'a' 

2. The int is converted to a char .

    char ch = 'a'; 

3. The char ch is converted to an int x . In theory there could be a loss of data going from char to int **, but given the overwhelming implementations, there is none. Typical examples: If char is signed in the range -128 to 127, this maps well into int . If char is unsigned in the range 0 to 255, this also maps well into int .

    int x; x = ch; 

4. printf("%c", x) uses the int x value passed to it, converts it to unsigned char and then prints that character. (C11dr §7.21.6.1 8 @haccks) Note there is no conversion of x due to the usual conversion of variadic parameters as x is all ready an int .

    printf("x=%c", x); 

---

** char and int could be the same size and char is unsigned with a positive range more than int . This is the one potential problem with casting char to int although typically there is not loss of data. This could be further complicated should char have range like 0 to 2³²-1 and int with a range of -(2³¹-1) to +(2³¹-1). I know of no such machine.

Answer 2

Yes, casting integer types to bigger integer types is always safe.

Standard library's *getc (fgetc, getchar, ...) functions do just that--they read unsigned chars internally and cast them to int because int provides additional room for encoding EOF (end of file, usually EOF==-1).

Answer 3

是的，因为int大于char ，但出于相同的原因，使用char代替int并不安全。

Answer 4

it is safe here because char is converted to int anyway when calling printf .

see C++ variadic arguments

Answer 5

What you are doing is first =

int x = ch => Assigning the ascii value of the char to an int

And finally : printf("x=%c", x); => Printing the ascii value as a char, which will print the actual char that correspond to that value. So yeah it's safe to do that, it's a totally predicatable behaviour.
But safe does not mean useful as integer is bigger than char, usually we do the inverse to save some memory.