What is the purpose of sizeof? When I delete the sizeof it shows the error about IntelliSense: argument of type "char *" is incompatible with parameter of type "int" but the program still can run.
Code:#include <stdio.h> #include <string.h> #include <stdlib.h> int main() { char buf[20]; char *a; printf ("Please enter a line of text, max %d characters\n", buf); fgets(buf, buf, stdin); a = strchr(buf, '\n'); *a= '\0'; printf ("Thank you, you entered >%s<\n", buf); system("pause"); }
sizeof is a compile-time operator that computes the size, in characters, of its argument. It works on any non-void type (and a pointer to void is a non-void type), as well as on anything with a type (for example, variables). sizeof(char), which is equivalent to sizeof char, is defined to be 1.
In your code, sizeof(buf) will be 20, since buf is an array of 20 char. sizeof(a) is an implementation defined value (since the size of a pointer is compiler dependent). sizeof(*a) will be 1 (as a is a pointer to char, so *a is a char).
A common use of sizeof() is when dynamically allocating memory. malloc(n*sizeof(X)), if it succeeds, allocates enough memory to hold n X's.
Since sizeof() yields a value of type size_t (an unsigned integral type) it should not be printed using printf()'s %s format. That is probably the reason for the error. Technically, IIRC, there is no direct way of printing a size_t in C other than converting it to unsigned long, printing that using %lu, and praying.
You definitly need a sizeof here.
The size of will find the size of buf, which in your case is 10 bytes. So that the fgets will only read 10 bytes of the user avoiding buffer overflow.Code:fgets(buf, sizeof(buf), stdin);
ssharish
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Is this good practice to put sizeof in this line of code or is redundant?
Code:printf ("Please enter a line of text, max %d characters\n", sizeof(buf));
Is it good practice to walk to an apple tree or is it redundant?
The answer to this question, like the answer to yours, depends on what you are trying to achieve. If you want to pick an apple, walking to an apple tree is good practice. If you don't want to pick an apple, walking to an apple tree is unnecessary (and possibly redundant).
So, the codein FAQ > Get a line of text from the user/keyboard (C) - Cprogramming.com is redundant.Code:printf ("Please enter a line of text, max %d characters\n", sizeof(buf));
The point is, if you want to tell the user the maximum amount of characters to enter, the line is necessary and therefore -- by definition -- not redundant. If you don't want to tell the user this information, then yes, it's unnecessary and therefore redundant.
And printing that information, redundant aspect aside, doesn't buy you out of verifying unknown input.
Soma
No, absolutely not.Originally Posted by ulti-killer
So, the codein FAQ > Get a line of text from the user/keyboard (C) - Cprogramming.com is redundant.Code:printf ("Please enter a line of text, max %d characters\n", sizeof(buf));
Redundant would mean that the effect is the same with or without it. If you had run the program with and without it then you would notice that with and without clearly produces different results. So no, of course it's not redundant.
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