How can I use a char array in a switch statement?
If I do it this way,
switch (argv[i]) {
case '-': .....
default: ......
}
I get an error:
switch quantity not an integer.
3 Answers
In switch, the expression must be of "an integral type"
Do a set of if/else instead of switch.
3 Comments
Keith Thompson
The expression "shall have integer type". The question is tagged C, and C doesn't have class types or maps.
Huy
@KeithThompson Thanks for your comment, I have modified my answer
M.M
This doesn't really help unless you provide a code sample
You can't really do that.
argv[i] is a memory address, a number, it's not a string and can't be implicitly compared to another "string" (either literal of char array). Withing a switch statement, only integral type can be compared. You can use a specific character inside that "string":
switch(argv[i][0]){
case '-': .....
default: ......
}
but that's probably not what you want...
The straight forward solution is to use a group of if() ... else if() ... statements:
if(!strcmp(argv[i], "-")) {
//...
} else if(!strcmp(argv[i], "some other value")) {
//...
} else {
// non of these...
}
9 Comments
Keith Thompson
"
argv[i] is a memory address" ... right ... ", a number" -- nope. An address is not a number. And I'm not sure what you mean by "comparable string". The expression in a switch statement has to be of integer type.
Amit
@KeithThompson an address is materialized as a number. It can freely be assigned to an integer type for example. The "comparable string" part is indeed confusing. I'll rephrase...
Keith Thompson
No, an address cannot be freely assigned to an integer type. It might (or might not) have a similar representation, and it can be converted with an explicit cast, but the language makes a strong distinction between pointers and numbers.
Amit
@KeithThompson - I'll cherry pick the part the part to support my argument: "Any pointer type may be converted to an integer type". Of course, thats not always meaningful and the other direction (int -> pointer) is more dangerous, but it is assignable.
Keith Thompson
Yes, may be converted. You can't assign a pointer to an integer; you can convert a pointer to an integer (and the conversion may be non-trivial), and then assign the result. The most important point is this: pointers are not integers.
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According to C11:
6.8.4.2 The switch statement
1 The controlling expression of a switch statement shall have integer type.
So unfortunately, one can never use non-integer types in a switch statement.
Also, argv[1] is a char* actually. This is easy to understand, because int main(int argc, char *argv[]) is just equivalent to int main(int argc, char **argv)
1 Comment
Keith Thompson
argv[I] is a char*, not an array.
**char... you can't do:switch(char*)it just is the way the language is structured... if you are working on parsing argv for normal switches, you should look atman 3 getopt