2 files changed, 32 insertions, 0 deletions
diff --git a/absl/strings/numbers.cc b/absl/strings/numbers.cc
index e6bf44ce..966d94bd 100644
--- a/absl/strings/numbers.cc
+++ b/absl/strings/numbers.cc
@@ -46,8 +46,13 @@ ABSL_NAMESPACE_BEGIN
 bool SimpleAtof(absl::string_view str, float* out) {
   *out = 0.0;
   str = StripAsciiWhitespace(str);
+  // std::from_chars doesn't accept an initial +, but SimpleAtof does, so if one
+  // is present, skip it, while avoiding accepting "+-0" as valid.
   if (!str.empty() && str[0] == '+') {
     str.remove_prefix(1);
+    if (!str.empty() && str[0] == '-') {
+      return false;
+    }
   }
   auto result = absl::from_chars(str.data(), str.data() + str.size(), *out);
   if (result.ec == std::errc::invalid_argument) {
@@ -72,8 +77,13 @@ bool SimpleAtof(absl::string_view str, float* out) {
 bool SimpleAtod(absl::string_view str, double* out) {
   *out = 0.0;
   str = StripAsciiWhitespace(str);
+  // std::from_chars doesn't accept an initial +, but SimpleAtod does, so if one
+  // is present, skip it, while avoiding accepting "+-0" as valid.
   if (!str.empty() && str[0] == '+') {
     str.remove_prefix(1);
+    if (!str.empty() && str[0] == '-') {
+      return false;
+    }
   }
   auto result = absl::from_chars(str.data(), str.data() + str.size(), *out);
   if (result.ec == std::errc::invalid_argument) {
diff --git a/absl/strings/numbers_test.cc b/absl/strings/numbers_test.cc
index 27616bf8..f3103106 100644
--- a/absl/strings/numbers_test.cc
+++ b/absl/strings/numbers_test.cc
@@ -392,6 +392,28 @@ TEST(NumbersTest, Atod) {
   EXPECT_TRUE(std::isnan(d));
 }
 
+TEST(NumbersTest, Prefixes) {
+  double d;
+  EXPECT_FALSE(absl::SimpleAtod("++1", &d));
+  EXPECT_FALSE(absl::SimpleAtod("+-1", &d));
+  EXPECT_FALSE(absl::SimpleAtod("-+1", &d));
+  EXPECT_FALSE(absl::SimpleAtod("--1", &d));
+  EXPECT_TRUE(absl::SimpleAtod("-1", &d));
+  EXPECT_EQ(d, -1.);
+  EXPECT_TRUE(absl::SimpleAtod("+1", &d));
+  EXPECT_EQ(d, +1.);
+
+  float f;
+  EXPECT_FALSE(absl::SimpleAtof("++1", &f));
+  EXPECT_FALSE(absl::SimpleAtof("+-1", &f));
+  EXPECT_FALSE(absl::SimpleAtof("-+1", &f));
+  EXPECT_FALSE(absl::SimpleAtof("--1", &f));
+  EXPECT_TRUE(absl::SimpleAtof("-1", &f));
+  EXPECT_EQ(f, -1.f);
+  EXPECT_TRUE(absl::SimpleAtof("+1", &f));
+  EXPECT_EQ(f, +1.f);
+}
+
 TEST(NumbersTest, Atoenum) {
   enum E01 {
     E01_zero = 0,