by e.g. "echo DEVELOPER=1 >>config.mak".
- We try to support a wide range of C compilers to compile Git with,
- including old ones. You should not use features from newer C
+ including old ones. As of Git v2.35.0 Git requires C99 (we check
+ "__STDC_VERSION__"). You should not use features from a newer C
standard, even if your compiler groks them.
- There are a few exceptions to this guideline:
+ New C99 features have been phased in gradually, if something's new
+ in C99 but not used yet don't assume that it's safe to use, some
+ compilers we target have only partial support for it. These are
+ considered safe to use:
+
+ . since around 2007 with 2b6854c863a, we have been using
+ initializer elements which are not computable at load time. E.g.:
+
+ const char *args[] = {"constant", variable, NULL};
. since early 2012 with e1327023ea, we have been using an enum
definition whose last element is followed by a comma. This, like
. since early 2021 with 765dc168882, we have been using variadic
macros, mostly for printf-like trace and debug macros.
- These used to be forbidden, but we have not heard any breakage
- report, and they are assumed to be safe.
+ . since late 2021 with 44ba10d6, we have had variables declared in
+ the for loop "for (int i = 0; i < 10; i++)".
+
+ New C99 features that we cannot use yet:
+
+ . %z and %zu as a printf() argument for a size_t (the %z being for
+ the POSIX-specific ssize_t). Instead you should use
+ printf("%"PRIuMAX, (uintmax_t)v). These days the MSVC version we
+ rely on supports %z, but the C library used by MinGW does not.
+
+ . Shorthand like ".a.b = *c" in struct initializations is known to
+ trip up an older IBM XLC version, use ".a = { .b = *c }" instead.
+ See the 33665d98 (reftable: make assignments portable to AIX xlc
+ v12.01, 2022-03-28).
- Variables have to be declared at the beginning of the block, before
the first statement (i.e. -Wdeclaration-after-statement).
- - Declaring a variable in the for loop "for (int i = 0; i < 10; i++)"
- is still not allowed in this codebase. We are in the process of
- allowing it by waiting to see that 44ba10d6 (revision: use C99
- declaration of variable in for() loop, 2021-11-14) does not get
- complaints. Let's revisit this around November 2022.
-
- NULL pointers shall be written as NULL, not as 0.
- When declaring pointers, the star sides with the variable
void show_object_with_name(FILE *out, struct object *obj, const char *name)
{
fprintf(out, "%s ", oid_to_hex(&obj->oid));
- /*
- * This "for (const char *p = ..." is made as a first step towards
- * making use of such declarations elsewhere in our codebase. If
- * it causes compilation problems on your platform, please report
- * it to the Git mailing list at git@vger.kernel.org. In the meantime,
- * adding -std=gnu99 to CFLAGS may help if you are with older GCC.
- */
for (const char *p = name; *p && *p != '\n'; p++)
fputc(*p, out);
fputc('\n', out);