Most Common problems in C

**Bayint Naung** · 06-02-2010

For casting return value of malloc(), it's not necessary.
There's no point to cast unless you are going to use C++ compiler.
But, I'd prefer

Code:

       foo_t *p;      
      p = malloc( sizeof(foo_t) );
       // prefer
       p = malloc( sizeof(*p) );

      #define NELEM(array)       ( sizeof(array) / sizeof( foo_t) )
      // prefer
      #define NELEM(array)       ( sizeof(array) / sizeof( (array)[0]) )

**quzah** · 06-02-2010

Originally Posted by Bayint Naung

But, I'd prefer

Code:

       foo_t *p;
       p = malloc( sizeof(*p) );
       // prefer
       p = malloc( sizeof(foo_t) ); /* 1 */

      #define NELEM(array)       ( sizeof(array) / sizeof( foo_t) )
      // prefer
      #define NELEM(array)       ( sizeof(array) / sizeof( (array)[0]) ) /* 2 */

1. While it may be your preference, the former method is less accident prone, and is easier to maintain (ie: you don't have to ever change it). If you go back and substitute foo_t for bar_t, you have to chase down all of your malloc calls, and change them too. If you use the first method, you don't have to.

2. Neither of those methods work for arrays declared outside the current scope.

Quzah.

**Bayint Naung** · 06-02-2010

Originally Posted by claudiu

Well, fueled by MK27's relentless optimism I decided it's time to drop the skepticism and add my own thing here. One thing I see here everyday and is driving me nutz, although not a mistake per say is the casting of malloc().

Another thing, which is not necessarily related to C is the confusion between an IDE and a compiler. Most people will come and say... "ohh I compilez my codez with Eclipse and needz helpz cuz deadline iz tomorrow!".

I still remember one post.
" I compile this codel from online tutorial and my compiler gives error.
1.

Code:

for(int i = 0; i < n; i++) {        
...
}

The problem is most newbies don't know it's only supported in C99.
The worst thing is most will manage to write code that will compile.
2.

Code:

if( 0 < n < 10 ) {

But I find that gcc (if enable warning) will give warning.
1. compile with gcc -Wall foo.c
bar.c:100: error: ‘for’ loop initial declarations are only allowed in C99 mode
bar.c:100: note: use option -std=c99 or -std=gnu99 to compile your code

2. gcc -Wall foo.c
bar.c:106: warning: comparisons like ‘X<=Y<=Z’ do not have their mathematical meaning

**Bayint Naung** · 06-02-2010

1. While it may be your preference, the former method is less accident prone, and is easier to maintain (ie: you don't have to ever change it). If you go back and substitute foo_t for bar_t, you have to chase down all of your malloc calls, and change them too. If you use the first method, you don't have to.

2. Neither of those methods work for arrays declared outside the current scope.

1. it's a misteaks!

2. YES

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