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add support for padding string and char arguments #13

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Merged
tjol merged 1 commit into from
Apr 30, 2025
Merged

add support for padding string and char arguments #13

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46 changes: 44 additions & 2 deletions src/format.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -472,7 +472,29 @@ impl Printf for f32 {
impl Printf for &str {
fn format(&self, spec: &ConversionSpecifier) -> Result<String> {
if spec.conversion_type == ConversionType::String {
Ok((*self).to_owned())
let mut s = String::new();

let width: usize = match spec.width {
NumericParam::Literal(w) => w,
_ => {
return Err(PrintfError::Unknown); // should not happen at this point!!
}
}
.try_into()
.unwrap_or_default();

if spec.left_adj {
s.push_str(self);
while s.len() < width {
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@tjol tjol Apr 30, 2025

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It's a shame String has no resize() method like Vec does... (but I suppose that wouldn't work well with multi-byte characters)

s.push(' ');
}
} else {
while s.len() + self.len() < width {
s.push(' ');
}
s.push_str(self);
}
Ok(s)
} else {
Err(PrintfError::WrongType)
}
Expand All @@ -486,7 +508,27 @@ impl Printf for char {
fn format(&self, spec: &ConversionSpecifier) -> Result<String> {
if spec.conversion_type == ConversionType::Char {
let mut s = String::new();
s.push(*self);

let width: usize = match spec.width {
NumericParam::Literal(w) => w,
_ => {
return Err(PrintfError::Unknown); // should not happen at this point!!
}
}
.try_into()
.unwrap_or_default();

if spec.left_adj {
s.push(*self);
while s.len() < width {
s.push(' ');
}
} else {
while s.len() + self.len_utf8() < width {
s.push(' ');
}
s.push(*self);
}
Ok(s)
} else {
Err(PrintfError::WrongType)
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6 changes: 6 additions & 0 deletions tests/compare_to_libc.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -116,6 +116,10 @@ fn test_str() {
let c_string = CString::new("test").unwrap();
check_fmt("%s", c_string.as_c_str());
check_fmt("%s", c_string);
check_fmt_s("%4s", "A");
check_fmt_s("%4s", "𒀀"); // multi-byte character test (4 bytes)
check_fmt_s("%-4sX", "A");
check_fmt_s("%-4sX", "𒀀"); // multi-byte character test (4 bytes)
}

#[test]
Expand All @@ -125,6 +129,8 @@ fn test_char() {
check_fmt("%c", b'x' as c_char);
check_fmt("%c", u16::try_from('x').unwrap());
check_fmt("%c", u32::try_from('x').unwrap());
check_fmt("%4c", 'A');
check_fmt("%-4cX", 'A');
}

#[test]
Expand Down