Avoid StringWriter cast and string format

src/header/arpa_inet/mod.rs

@@ -15,6 +15,7 @@ use crate::{
         netinet_in::{INADDR_NONE, in_addr, in_addr_t},
         sys_socket::{constants::AF_INET, socklen_t},
     },
+    io::Write,
     platform::{
         self,
         types::{c_char, c_int, c_void},
@@ -193,10 +194,12 @@ pub unsafe extern "C" fn inet_ntop(
                 4,
             )
         };
-        let addr = format!("{}.{}.{}.{}\0", s_addr[0], s_addr[1], s_addr[2], s_addr[3]);
-        unsafe {
-            ptr::copy(addr.as_ptr().cast::<c_char>(), dst, addr.len());
-        }
+        let mut w = platform::StringWriter(dst, size as usize);
+        let _ = write!(
+            w,
+            "{}.{}.{}.{}\0",
+            s_addr[0], s_addr[1], s_addr[2], s_addr[3]
+        );
         dst
     }
 }

src/header/monetary/strfmon.rs

@@ -2,7 +2,7 @@ use crate::platform::types::{c_char, size_t, ssize_t};
 
 use super::{DEFAULT_MONETARY, FormatFlags, LocaleMonetaryInfo, apply_grouping};
 use alloc::string::{String, ToString};
-use core::{ffi::CStr, slice};
+use core::{ffi::CStr, fmt::Write, slice};
 use libm::{fabs, pow, round, trunc};
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strfmon.html>.
@@ -284,7 +284,7 @@ fn format_monetary(
     if frac_digits > 0 {
         result.push_str(monetary.mon_decimal_point);
         // Zero-pad fractional part to the specified width
-        result.push_str(&format!("{:0>width$}", frac_part, width = frac_digits));
+        let _ = write!(result, "{:0>width$}", frac_part, width = frac_digits);
     }
 
     // 12) if the currency symbol follows the amount, add it now

src/header/stdio/mod.rs

@@ -1479,7 +1479,7 @@ pub unsafe extern "C" fn vsnprintf(
 ) -> c_int {
     unsafe {
         printf::printf(
-            &mut platform::StringWriter(s.cast::<u8>(), n),
+            &mut platform::StringWriter(s, n),
             CStr::from_ptr(format),
             ap,
         )
@@ -1496,7 +1496,7 @@ pub unsafe extern "C" fn snprintf(
 ) -> c_int {
     unsafe {
         printf::printf(
-            &mut platform::StringWriter(s.cast::<u8>(), n),
+            &mut platform::StringWriter(s, n),
             CStr::from_ptr(format),
             __valist.as_va_list(),
         )

src/header/string/mod.rs

@@ -359,17 +359,16 @@ pub unsafe extern "C" fn strdup(s1: *const c_char) -> *mut c_char {
 pub unsafe extern "C" fn strerror_l(errnum: c_int, _loc: locale_t) -> *mut c_char {
     use core::fmt::Write;
 
-    static strerror_buf: RawCell<[u8; STRERROR_MAX]> = RawCell::new([0; STRERROR_MAX]);
-    let mut w = platform::StringWriter(unsafe { strerror_buf.unsafe_mut().as_mut_ptr() }, unsafe {
-        strerror_buf.unsafe_ref().len()
-    });
+    static STRERROR_BUF: RawCell<[c_char; STRERROR_MAX]> = RawCell::new([0; STRERROR_MAX]);
+    let strerror_ptr = unsafe { STRERROR_BUF.unsafe_mut().as_mut_ptr() };
+    let mut w = platform::StringWriter(strerror_ptr, STRERROR_MAX);
 
     let _ = match STR_ERROR.get(errnum as usize) {
         Some(e) => w.write_str(e),
         None => w.write_fmt(format_args!("Unknown error {}", errnum)),
     };
 
-    (unsafe { strerror_buf.unsafe_mut().as_mut_ptr() }).cast::<c_char>()
+    strerror_ptr
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/strerror.html>.

src/header/time/mod.rs

@@ -499,13 +499,8 @@ pub unsafe extern "C" fn strftime(
     format: *const c_char,
     timeptr: *const tm,
 ) -> size_t {
-    let ret = unsafe {
-        strftime::strftime(
-            &mut platform::StringWriter(s.cast::<u8>(), maxsize),
-            format,
-            timeptr,
-        )
-    };
+    let mut w = platform::StringWriter(s, maxsize);
+    let ret = unsafe { strftime::strftime(&mut w, format, timeptr) };
     if ret < maxsize { ret } else { 0 }
 }