On macOS 13.3.1, strtod() does not seem to respect the locale set using uselocale(), and does not process decimal points/commas correctly. Is this a bug in macOS? Is there a workaround?
Here's a test program that demonstrates that printf() and scanf() respect the decimal point setting, but strtod() does not.
#include <locale.h>
#include <xlocale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
int main() {
double x;
const char *num = "12.3";
char *end;
// First we set the locale globally to something that uses decimal
// commas instead of decimal points.
const char *locname = setlocale(LC_ALL, "de_DE");
struct lconv *lc = localeconv();
if (strcmp(lc->decimal_point, ",")) {
/* If decimal point is not a comma, presumably because the requested
* locale was not available, report locale information and quit. */
fprintf(stderr, "setlocale() returned '%s', decimal point is '%s'\n",
locname ? locname : "NULL",
lc->decimal_point);
abort();
}
// In this locale, printf() uses decimal commas, and both scanf() and strtod()
// assume decimal commas when reading numbers. Thus when reading 12.3, both
// of these function stop reading as soon as they reach the '.' character.
printf("Using locale with decimal comma:\n");
x = 0.0;
printf("%g\n", 12.3);
sscanf(num, "%lf", &x);
printf("%g\n", x);
x = strtod(num, &end);
printf("%g\n", x);
// Now we set the numeric local to use decimal points in a thread-local manner
// using the non-standard uselocale().
locale_t c_locale = newlocale(LC_NUMERIC_MASK, "C", NULL);
assert(c_locale != NULL);
uselocale(c_locale);
// Now both scanf() and strtod() should be assuming a decimal point,
// and both should read 12.3 in full.
printf("\nUsing locale with decimal point:\n");
x = 0.0;
printf("%g\n", 12.3);
sscanf("12.3", "%lf", &x);
printf("%g\n", x);
x = strtod(num, &end);
printf("%g\n", x);
return 0;
}
Output on macOS 10.14.6 is as I expect:
Using locale with decimal comma:
12,3
12
12
Using locale with decimal point:
12.3
12.3
12.3
Output on macOS 13.3.1:
Using locale with decimal comma:
12,3
12
12
Using locale with decimal point:
12.3
12.3
12
Notice that strtod() did not read past the decimal point.
Note: This was discovered as it causes the test suite of igraph to fail. The issue report is here.
