Are C Struct Members Initialized to Zero by Default?

Are Members of a C Struct Initialized to 0 by Default?

The values of uninitialized members of a C struct are not guaranteed to be 0. To explicitly initialize these members, use an initialization list:

struct Snapshot
{
    double x; 
    int y;
};

Snapshot s = {0, 0}; // Explicitly initialize members to 0

Alternatively, you can initialize the struct using the {} syntax:

Snapshot s = {}; // Value initializes all members to 0

Note that using {} for value initialization works recursively, even for nested structs:

struct Parent { Snapshot s; };
Parent p = {}; // Value initializes both p and p.s to 0

If the struct has constructors, you must explicitly initialize the members in those constructors:

struct Snapshot {
    int x;
    double y;
    Snapshot(): x(0), y(0) { } // Initialize members in the constructor
};

Alternatively, you can use the default value initialization syntax x(), y() to disregard the type and assign an appropriate initial value (0 for int, 0.0 for double, etc.):

Snapshot(): x(), y() { } // Value initializes both x and y to 0

This can be especially useful for templates.

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