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| Code Block | ||||
|---|---|---|---|---|
| ||||
int i1 = 10; /* Definition, external linkage */
static int i2 = 20; /* Definition, internal linkage */
extern int i3 = 30; /* Definition, external linkage */
int i4; /* Tentative definition, external linkage */
static int i5; /* Tentative definition, internal linkage */
int i1; /* Valid tentative definition */
int i2; /* Not valid, linkage disagreement with previous */
int i3; /* Valid tentative definition */
int i4; /* Valid tentative definition */
int i5; /* Not valid, linkage disagreement with previous */
int main(void) {
/* ... */
return 0;
}
|
Implementation Details
Microsoft Visual Studio 2008 and later provide warnings for this code at the default warning level (/W3), but earlier versions do not warn even at the highest diagnostic levels. The GCC compiler generates a fatal diagnostic for the conflicting definitions of i2 and i5.
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| Code Block | ||||
|---|---|---|---|---|
| ||||
int i1 = 10; /* Definition, external linkage */
static int i2 = 20; /* Definition, internal linkage */
extern int i3 = 30; /* Definition, external linkage */
int i4; /* Tentative definition, external linkage */
static int i5; /* Tentative definition, internal linkage */
int main(void) {
/* ... */
return 0;
}
|
Risk Assessment
Use of an identifier classified as both internally and externally linked causes undefined behavior.
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