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#include <stdio.h>
void f(void) {
if (sizeof(int) == sizeof(float)) {
float f = 0.0f;
int *ip = (int *)&f;
printf("float is %f\n", f);
(*ip)++; /* Diagnostic required */
printf("float is %f\n", f);
}
}
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#include <stdio.h>
void f(void) {
if (sizeof(int) == sizeof(float)) {
float f = 0.0f;
float *fp = &f;
printf("float is %f\n", f);
(*fp)++;
printf("float is %f\n", f);
}
}
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#include <stdio.h>
void func(void) {
short a[2];
a[0]=0x1111;
a[1]=0x1111;
*(int *)a = 0x22222222; /* Violation of aliasing rules */
printf("%x %x\n", a[0], a[1]);
/* ... */
} |
When translating this code, an implementation can assume that no access through an integer pointer can change the array a, consisting of shorts. Consequently, printf() may be called with the original values of a[0] and a[1]. The actual behavior is implementation-defined and can change with optimization level.
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#include <stdio.h>
void func(void) {
union {
short a[2];
int i;
} u;
u.a[0]=0x1111;
u.a[1]=0x1111;
u.i = 0x22222222;
printf("%x %x\n", u.a[0], u.a[1]);
/* ... */
} |
This code example now reliably outputs "2222 2222."
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