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Editorial Team
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Asked: 2026-05-13T20:56:59+00:00

AFAIK, extern keyword should be used for declaration and no value can be associated

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AFAIK, extern keyword should be used for declaration and no value can be associated with the variable being declared with extern keyword. But supposing I write a statement like

extern int i = 10;

Should the compiler flag an error for the same? I have seen some compilers being tolerant and ignoring this? Why is this so? What does the ‘C’ standard says about this?

EDIT: @All, Thanks for the answers. I have a doubt still though. Suppose I have the definition for this variable without the extern linkage in another file say a.c and I add this statement in b.c. Still is it Ok for the compiler not to flag an error? Does it come under redefintion?

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  1. Editorial Team

    That’s valid syntax, there is even an essentially identical example in the C99 standard. (See §6.9.2-4.)

    It’s true that the examples are not normative but I believe it was intended to be legal syntax. The compiler will often output a warning, because it doesn’t really accomplish anything.

    4 EXAMPLE 1

    int i1 = 1;             // definition, external linkage
static int i2 = 2;      // definition, internal linkage
extern int i3 = 3;      // definition, external linkage
int i4;                 // tentative definition, external linkage
static int i5;          // tentative definition, internal linkage
int i1;                 // valid tentative definition, refers to previous
int i2;                 // 6.2.2 renders undefined, linkage disagreement
int i3;                 // valid tentative definition, refers to previous
int i4;                 // valid tentative definition, refers to previous
int i5;                 // 6.2.2 renders undefined, linkage disagreement
extern int i1;          // refers to previous, whose linkage is external
extern int i2;          // refers to previous, whose linkage is internal
extern int i3;          // refers to previous, whose linkage is external
extern int i4;          // refers to previous, whose linkage is external
extern int i5;          // refers to previous, whose linkage is internal
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