C: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long int' [-Wformat=]

Meaning

%d is int, %ld is long, %lld is long long, %zu is size_t, %f/%lf are double, %s is char*, and %p expects void*. A wrong specifier reads the wrong number of bytes from the argument list. In C++ prefer std::cout or std::format.

Common causes

• %d used with long, size_t or long long
• %s given a std::string instead of c_str()
• Missing argument for a specifier, or an extra one
• %f used with float in scanf (needs %f for float but %lf for double)
• %p given a non-void pointer without a cast

Detailed fix by platform

Code examples

#include <stdio.h>
#include <stddef.h>

int main(void) {
    long big = 1234567890123L;
    size_t n = 42;
    printf("%ld %zu\n", big, n);    /* not %d for either of them */
    return 0;
}

How to diagnose

1. Specifier — Which % matches which argument?
2. Types — Exact type of each argument?
3. Count — Same number of specifiers and arguments?

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