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| Code Block | ||
|---|---|---|
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struct flexArrayStruct {
int num;
int data[1];
};
/* ... */
size_t array_size;
size_t i;
/* Spaceinitialize array_size */
/* space is allocated for the struct */
struct flexArrayStruct *structP
= (struct flexArrayStruct *)
malloc(sizeof(struct flexArrayStruct)
+ sizeof(int) * (ARRAYarray_SIZEsize - 1));
if (structP == NULL) {
/* handle malloc failure */
}
structP->num = SOME_NUMBER0;
/* Accessaccess data[] as if it had been allocated
* as data[ARRAYarray_SIZEsize] */
for (i = 0; i < ARRAYarray_SIZEsize; i++) {
structP->data[i] = i1;
}
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| Wiki Markup |
|---|
The problem with this code is that the only member that is guaranteed to be valid, by strict C99 definition, is {{structP->data\[0\]}}. Consequently, for all {{i > 0}}, the results of the assignment are undefined. |
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| Code Block | ||
|---|---|---|
| ||
struct flexArrayStruct{
int num;
int data[];
};
/* ... */
size_t array_size;
size_t i;
/* initialize array_size */
/* Space is allocated for the struct */
struct flexArrayStruct *structP
= (struct flexArrayStruct *)
malloc(sizeof(struct flexArrayStruct)
+ sizeof(int) * ARRAYarray_SIZEsize);
if (structP == NULL) {
/* handle malloc failure */
}
structP->num = SOME_NUMBER0;
/* Access data[] as if it had been allocated
* as data[ARRAYarray_SIZEsize] */
for (i = 0; i < ARRAYarray_SIZEsize; i++) {
structP->data[i] = i1;
}
|
| Wiki Markup |
|---|
This compliant solution allows the structure to be treated as if it had declared the member {{data\[\]}} to be {{data\[ARRAYarray_SIZEsize\]}} in a manner that conforms to the C99 standard. |
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