C Language Block Scope


An identifier has block scope if its corresponding declaration appears inside a block (parameter declaration in function definition apply). The scope ends at the end of the corresponding block.

No different entities with the same identifier can have the same scope, but scopes may overlap. In case of overlapping scopes the only visible one is the one declared in the innermost scope.

#include <stdio.h>

void test(int bar)                   // bar has scope test function block
    int foo = 5;                     // foo has scope test function block
        int bar = 10;                // bar has scope inner block, this overlaps with previous test:bar declaration, and it hides test:bar
        printf("%d %d\n", foo, bar); // 5 10
    }                                // end of scope for inner bar
    printf("%d %d\n", foo, bar);     // 5 5, here bar is test:bar
}                                    // end of scope for test:foo and test:bar

int main(void)
    int foo = 3;         // foo has scope main function block

    printf("%d\n", foo); // 3
    printf("%d\n", foo); // 3
    return 0;
}                        // end of scope for main:foo