backtrace_symbols_fmt
char **s = backtrace_symbols_fmt(trace, len, fmt);
return backtrace_symbols_fmt(trace, len, fmt);
char **backtrace_symbols_fmt(void *const *, size_t, const char *);
strings = backtrace_symbols_fmt(buffer, nptrs, "%n");
syms = backtrace_symbols_fmt(addr, frames, "%n");
syms = backtrace_symbols_fmt(addr, frames, "%n");
char **strings = backtrace_symbols_fmt(array, size, "%n");