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The size of a structure is not always equal to the sum of the sizes of its members. According to \[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\], |
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Non-Compliant Code Example
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This non-compliant code example assumes that the size of {{struct buffer}} is equal to the {{ |
struct buffer is equal to the sizeof(size_t) + (sizeof(char) * 50)}}, which may |
struct buffer may actually be a larger due to structure not be the case \[[Dowd|AA. C References#Dowd 06]\]. The size of {{struct buffer}} may actually be a larger due to structure padding. |
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struct buffer {
size_t size;
char buffer[50];
};
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void func(struct buffer *buf) {
/* assuming sizeof(size_t) is 4, sizeof(size_t)+sizeof(char)*50 equals 54 */
struct buffer *buf_cpy = malloc(sizeof(size_t)+(sizeof(char)*50));
if (buf_cpy == NULL) {
/* Handle malloc() error */
}
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/* with padding, sizeof(struct buffer) may be greater than 54, causing a
small amount of data to be written outside the bounds of the memory allocated */
memcpy(buf_cpy, buf, sizeof(struct buffer));
}
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