Trickies and Bugs in C

Posted on Edited on In Word count in article: 1.8k Reading time ≈ 2 mins.
the macro #define is the biggest hidden bug in c. You should always remember macro-function is like code paster. And it will slow down your system in some special situations, such as macro recursion. If you macro define some function use BIG characters. 
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#define FUN1(a,b) a*b
#define FUN2(a) a++;\
     a*=a;

int main(){
	int a = 2;
	int b = 3;
	FUN1(a,5+1); // => 2*5+1
        if(a>2)FUN2(a); //=> if(a>2) a++;a*=a;

	return 0;
}

strcpy() will copy “\0”, and it is dangerous when you copy two points.

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int main(){
	char str1[] = "abcd";
	char str2[] = "12";
	strcpy(str1,str2); // ok, str1 equals "12"
	char *st1 = "abcd";
	char *st2 = "12";
	strcpy(st1,st2); //crash!! st1 points to static const string
}

param as point or array style. Although they are differnt styles, they are the same.

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int size1(char a[]){
	cout << sizeof(a);
}
int size2(char* a){
	cout << sizeof(a);
}
int main(){
	char a[] = "abcdef";
	char *b = "abcdef";
	size1(a); //  => sizeof(char*)
	size1(b); //  => sizeof(char*)
	size2(a); //  => sizeof(char*)
	size2(b);//  => sizeof(char*)
	cout << sizeof(a)<<endl; // =>strlen(a)+1
	cout << sizeof(b)<<endl; // sizeof(char*)

}
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// There are 5 segments in codes, DATA, BSS, TEXT, heap, stack
// DATA stores all globel variables, and those variables are defined.
// BSS stores all globel variables, but those variables are not defined.
// const variables are in TEXT, and codes are in this segment also.
// heap store (malloc, calloc,realloc, new) data
// stack store function params, local variables.

int a; // a is in BSS
int b = 3; // b is in DATA
int fun(int c){ // c is in stack, when the function is called.
	return 0; 
}
int main(){
	const int c = 4; // c is in TEXT
	a = 4; // move to DATA
	int x = 4; // in stack
	int * p = malloc(sizeof(int)); // *p is in heap. but p is in stack.
	return 0;
}