adding C interface without dep to C++ standard lib

CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.14)
 
 
-project(fast_float VERSION 8.2.3 LANGUAGES CXX)
+project(fast_float VERSION 8.2.3 LANGUAGES CXX C)
 set(FASTFLOAT_CXX_STANDARD 11 CACHE STRING "the C++ standard to use for fastfloat")
 set(CMAKE_CXX_STANDARD ${FASTFLOAT_CXX_STANDARD})
 option(FASTFLOAT_TEST "Enable tests" OFF)
@@ -32,6 +32,8 @@ endif()
 
 add_library(fast_float INTERFACE)
 
+add_subdirectory(src)
+
 
 option(FASTFLOAT_BENCHMARKS "Enable benchmarks" OFF)
 if(FASTFLOAT_BENCHMARKS)

include/fast_float/fast_float_strtod.h

@@ -0,0 +1,31 @@
+#ifndef __FAST_FLOAT_STRTOD_H__
+#define __FAST_FLOAT_STRTOD_H__
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+/**
+ * @brief Convert a string to a double using the fast_float library. This is
+ * a C-compatible wrapper around the fast_float parsing functionality, designed
+ * to mimic the behavior of the standard strtod function.
+ *
+ * This function parses the initial portion of the null-terminated string `nptr`
+ * and converts it to a `double`, similar to the standard `strtod` function but
+ * utilizing the high-performance fast_float library for parsing.
+ *
+ * On successful conversion, the result is returned. If parsing fails, errno is
+ * set to EINVAL and 0.0 is returned.
+ *
+ * @param nptr   Pointer to the null-terminated string to be parsed.
+ * @param endptr If not NULL, a pointer to store the address of the first
+ *               character after the parsed number. If parsing fails, it points
+ *               to the beginning of the string.
+ * @return       The converted double value on success, or 0.0 on failure.
+ */
+double fast_float_strtod(const char *in, char **out);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* __FAST_FLOAT_STRTOD_H__ */

src/CMakeLists.txt

@@ -0,0 +1,14 @@
+add_library(fast_float_strtod STATIC fast_float_strtod.cpp)
+target_link_libraries(fast_float_strtod PRIVATE fast_float)
+
+if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")
+    target_link_options(fast_float_strtod PRIVATE -nostdlib++)
+endif()
+
+add_library(FastFloat::fast_float_strtod ALIAS fast_float_strtod)
+target_include_directories(
+  fast_float_strtod
+  INTERFACE
+    $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
+    $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+)

src/fast_float_strtod.cpp

@@ -0,0 +1,24 @@
+#include "fast_float/fast_float_strtod.h"
+#include "fast_float/fast_float.h"
+#include <cerrno>
+#include <cstring>
+#include <system_error>
+
+extern "C" double fast_float_strtod(const char *nptr, char **endptr) {
+  double result = 0.0;
+
+  // Parse the string using fast_float's from_chars function
+  auto parse_result = fast_float::from_chars(nptr, nptr + strlen(nptr), result);
+
+  // Check if parsing encountered an error
+  if (parse_result.ec != std::errc{}) {
+    errno = EINVAL;
+  }
+
+  // Update endptr if provided
+  if (endptr != nullptr) {
+    *endptr = const_cast<char *>(parse_result.ptr);
+  }
+
+  return result;
+}

tests/CMakeLists.txt

@@ -108,3 +108,10 @@ endif(FASTFLOAT_EXHAUSTIVE)
 
 add_subdirectory(build_tests)
 add_subdirectory(bloat_analysis)
+
+add_executable(strtod_test strtod_test.c)
+if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")
+    target_link_options(strtod_test PUBLIC -nostdlib++)
+endif()
+target_link_libraries(strtod_test PUBLIC fast_float_strtod)
+add_test(NAME strtod_test COMMAND strtod_test)

tests/strtod_test.c

@@ -0,0 +1,28 @@
+#include "fast_float/fast_float_strtod.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+
+int main() {
+    // Test successful conversion
+    const char *str1 = "3.14159";
+    char *end1;
+    errno = 0;
+    double d1 = fast_float_strtod(str1, &end1);
+    printf("Input: %s\n", str1);
+    printf("Converted: %f\n", d1);
+    printf("End pointer: %s\n", end1);
+    printf("errno: %d\n", errno);
+
+    // Test invalid input
+    const char *str2 = "invalid";
+    char *end2;
+    errno = 0;
+    double d2 = fast_float_strtod(str2, &end2);
+    printf("\nInput: %s\n", str2);
+    printf("Converted: %f\n", d2);
+    printf("End pointer: %s\n", end2);
+    printf("errno: %d\n", errno);
+
+    return 0;
+}