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This non-compliant code example assumes that the size of {{struct buffer}} is equal to the {{sizeof(size_t) + (sizeof(char) * 50)}}of its individual components, which may not be the case \[[Dowd 06|AA. C References#Dowd 06]\]. The size of {{struct buffer}} may actually be larger due to structure padding. |
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struct buffer {
size_t size;
char bufferC[50];
};
/* ... */
void func(struct buffer *buf) {
/* assumingAssumes sizeof(size_t struct buffer) is= 4, sizeof( size_t) + 50 * sizeof( char)*50 equals= 54 */
struct buffer *buf_cpy = (struct buffer *)malloc(sizeof(size_t)+(sizeof(char)*50))54);
if (buf_cpy == NULL) {
/* Handle malloc() error */
}
/*
* with padding, sizeof(struct buffer) may be greater than 54, causing
* some data to be written outside the bounds of the memory allocated
*/
memcpy(buf_cpy, buf, sizeof(struct buffer));
/* ... */
free(buf_cpy);
}
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Accounting for structure padding prevents these types of errors.
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enum {buffer_size = 50};
struct buffer {
size_t size;
char bufferC[50buffer_size];
};
/* ... */
void func(struct buffer *buf) {
struct buffer *buf_cpy = (struct buffer *)malloc(sizeof(struct buffer));
if (buf_cpy == NULL) {
/* Handle malloc() error */
}
/* ... */
memcpy(buf_cpy, buf, sizeof(struct buffer));
/* ... */
free(buf_cpy);
}
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