for example is there any difference between
#define LIMIT 100 and
int LIMIT= 100; If not is there any use scenario in which on can be used but the other can't?
- 3Any scenario where an integral constant expression is requiredStoryTeller - Unslander Monica– StoryTeller - Unslander Monica2017-07-17 10:24:07 +00:00Commented Jul 17, 2017 at 10:24
- One defines a preprocessor macro, and the other defines a variable. Preprocessor macros are used to replace parts of the code, and are compile-time only constructs. Variables exists as entities in the program, and can change value at run-time. If you need a pointer to a variable, then a macro can't be used. Variables can't be used when compile-time constants are expected.Some programmer dude– Some programmer dude2017-07-17 10:24:49 +00:00Commented Jul 17, 2017 at 10:24
- In the first case LIMIT is a constant. And it will be "replaced" with the value 100 before compile. You can also write "const int LIMIT = 100;" to declare a constantAnoroah– Anoroah2017-07-17 10:25:03 +00:00Commented Jul 17, 2017 at 10:25
- If you feel that one of the answers answered your question, please accept it to make this question more helpful for future users.Akira– Akira2017-08-02 07:31:47 +00:00Commented Aug 2, 2017 at 7:31
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2 Answers
The first one defines a preprocessor macro which will be replaced to its value everywhere in the code during preprocessing.
#define SIZE 4 int main() { int matrix_1[SIZE][SIZE] = { 0 }; int* array = malloc(SIZE * sizeof(int)); /* ... */ } The value of SIZE cannot be changed at run-time. After preprocessing the code above will be changed to the following:
int main() { int matrix_1[4][4] = { 0 }; int* array = malloc(4 * sizeof(int)); /* ... */ } The second one initializes an int variable which will be allocated on the stack and you can modify it on run-time.
int main() { int size = 4; size = 12; /* size in now 12 */ int* array = malloc(size * sizeof(int)); /* ... */ } The size cannot be used in contexts where an integer constant is required, e.g. as a size of a bit field, as a value of an enum constant, as case label of a switch statement, etc.
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#define LIMIT 100 define LIMIT as an integer constant while int LIMIT= 100; declare it as an integer variable.
