▶ 内存泄漏

清单 1. 简单的潜在堆内存丢失和缓冲区覆盖

void f1(char *explanation)
{ 
  char p1;
  p1 = malloc(100); 
  (void) sprintf(p1, "The f1 error occurred because of '%s'.", explanation); local_log(p1);
}

清单 2. 来自资源错误管理的潜在堆内存丢失

int getkey(char *filename)
{ 
     FILE *fp; 
     int key;
     fp = fopen(filename, "r");
     fscanf(fp, "%d", &key); 
     return key;
}

fopen的语义需要配对的 fclose（）。在没有 fclose()的情况下，C 标准不能指定发生的情况时，很可能是内存泄漏。其他资源(如信号量、网络句柄、数据库连接等)同样值得考虑。

void f2(int datum)
{ 
     int *p2;
     /* Uh-oh! No one has initialized p2. */ 
     *p2 = datum; 
     ...        
}

清单 4. 两个错误的内存释放

/* Allocate once, free twice. */
void f3()
{ 
  char *p;
  p = malloc(10); 
  ... 
  free(p);
  ... free(p); 
}

 /* Allocate zero times, free once. */
void f4()
{ 
    char *p;
    /* Note that p remains uninitialized here. */ 
   free(p);
}

清单 5. 悬空指针

void f8() 
 { 
  struct x *xp;
  xp = (struct x *) malloc(sizeof (struct x)); 
  xp.q = 13; 
  ... 
  free(xp); 
  ... 
  /* Problem! There's no guarantee that the memory block to which xp points hasn't been overwritten. */ 
  return xp.q; 
}

勤奋和自律可以让这些错误造成的影响降至最低限度。

下面我们介绍一下您可以采用的几个特定步骤;

我在各种组织中处理它们的经验是，至少可以一定程度上持续减少内存错误。

编码风格是最重要的，我还从没有看到过其他任何作者对此加以强调。影响资源(特别是内存)的函数和方法需要显式地解释本身。下面是有关标头、注释或名称的一些示例(请参见清单 6)。

/********* ...
* Note that any function invoking protected_file_read()
* assumes responsibility eventually to fclose() its
* return value, UNLESS that value is NULL.
*/
FILE *protected_file_read(char *filename)
{ 
  FILE *fp;
  fp = fopen(filename, "r"); 
  if (fp) {... } else {... } return fp;
}
/******** ...
* Note that the return value of get_message points to a
* fixed memory location. Do NOT free() it; remember to
* make a copy if it must be retained ...
*/
char *get_message()
{ 
   static char this_buffer[400];
   ... 
   (void) sprintf(this_buffer, ...); 
   return this_buffer; 
}

/********* ...
* While this function uses heap memory, and so 
* temporarily might expand the over-all memory
* footprint, it properly cleans up after itself.
* *******
*/ 
int f6(char *item1)
{ 
   my_class c1; 
   int result; 
   ... c1 = new my_class(item1); 
   ... result = c1.x; 
   delete c1; 
   return result;}
/********* ...
* Note that f8() is documented to return a value
* which needs to be returned to heap; as f7 thinly
* wraps f8, any code which invokes f7() must be* careful to free() the return value.
*********/
int *f7()
{ 
   int *p;
   p = f8(...); 
   ... return p;
}

硬件检查器在这整个领域中，我始终认为最有用并且投资回报率最大的是考虑改进源代码的风格。它不需要昂贵的代价或严格的形式;

可以始终取消与内存无关的段的注释，但影响内存的定义当然需要显式注释。

添加几个简单的单词可使内存结果更清楚，并且内存编程会得到改进。

static char *important_pointer = NULL;
void f9()
{ 
    if (!important_pointer)
       important_pointer = malloc(IMPORTANT_SIZE); 
    ... 
    if (condition)
    /* Ooops! We just lost the reference  important_pointer already held. */
    important_pointer = malloc(DIFFERENT_SIZE);
    ...        
}

int main()
{ 
   char p[5]; 
   strcpy(p, "Hello, world."); 
   puts(p);
}