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In this noncompliant code example, an array of long is allocated and assigned to p. This example also checks for unsigned integer overflow in compliance with INT32-C. Ensure that operations on signed integers do not result in overflow. The code also ensures that len is not equal to zero. (See MEM04-C. Do not perform zero-length allocations.) However, sizeof(int) is used to size the allocated memory. If sizeof(long) is larger than sizeof(int), then an insufficient amount of memory is allocated.

#include <stdlib.h>
 
void function(size_t len) {
   long *p;
   if (len == 0 || len > SIZE_MAX / sizeof(long)) {
      /* Handle overflow */
   }
   p = (long *)malloc(len * sizeof(int));
   if (p == NULL) {
      /* Handle error */
   }
   free(p);
}

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Compliant Solution (Size Calculation)

To correct the noncompliant code example, This compliant solution uses sizeof(long) is used to  to correctly size the memory allocation:

#include <stdlib.h>
void function(size_t len) {
   long *p;
   if (len == 0 || len > SIZE_MAX / sizeof(long)) {
      /* Handle overflow */
   }
   p = (long *)malloc(len * sizeof(long));
   if (p == NULL) {
      /* Handle error */
   }
   free(p);
}

Compliant Solution (Size Calculation)

#include <stdlib.h>
 
void function(size_t len) {
   long *p;
   if (len == 0 || len > SIZE_MAX / sizeof(*p)) {
      /* Handle overflow */
   }
   p = (long *)malloc(len * sizeof(*p));
   if (p == NULL) {
      /* Handle error */
   }
   free(p);
}

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Noncompliant Code Example

In this noncompliant code example, too little space is allocated for a struct tm object because the size of the pointer is being used to determine the size of the pointed-to object. This is a demonstration of EXP01-C. Do not take the size of a pointer to determine the size of the pointed-to type.

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 In this compliant solution, the correct amount of memory is allocated for the struct tm object. When allocating  space for a single object, passing the (dereferenced) pointer type to the sizeof operator is a simple way to allocate sufficient memory.

#include <time.h>
 
struct tm *make_tm(int year, int mon, int day, int hour,
                   int min, int sec) {
  struct tm *tmb;
  tmb = (struct tm *)malloc(sizeof(*tmb));
  if (tmb == NULL) {
    return NULL;
  }
  tmb->tm_sec = sec;
  tmb->tm_min = min;
  tmb->tm_hour = hour;
  tmb->tm_mday = day;
  tmb->tm_mon = mon;
  tmb->tm_year = year;
  return tmb;
}

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