From: Junio C Hamano Date: Thu, 26 Feb 2026 20:58:48 GMT Subject: Re: [RFC PATCH 02/14] strvec: introduce `strvec_init_alloc()` Message-ID: In-Reply-To: Junio C Hamano writes: > Taylor Blau writes: > >> When the caller knows upfront how many elements will be pushed onto a >> `strvec`, it is useful to pre-allocate enough space in the array to fit >> that many elements (and one additional slot to store NULL, indicating >> the end of the list.) >> >> Introduce `strvec_init_alloc()`, which allocates the backing array large >> enough to hold `alloc` elements and the termination marker without >> further reallocation. >> >> Signed-off-by: Taylor Blau >> --- >> strvec.c | 7 +++++++ >> strvec.h | 5 +++++ >> 2 files changed, 12 insertions(+) >> >> diff --git a/strvec.c b/strvec.c >> index f8de79f5579..f7f32a53b56 100644 >> --- a/strvec.c >> +++ b/strvec.c >> @@ -10,6 +10,13 @@ void strvec_init(struct strvec *array) >> memcpy(array, &blank, sizeof(*array)); >> } >> >> +void strvec_init_alloc(struct strvec *array, size_t alloc) >> +{ >> + CALLOC_ARRAY(array->v, st_add(alloc, 1)); >> + array->nr = 0; >> + array->alloc = alloc + 1; >> +} > > It is not satisifying that strvec_init() does *not* become a thin > wrapper around this that says "my initial allocation is for zero > elements", but that cannot be done easily as a strvec that begins as > an empty one has a small optimization to avoid one-slot allocation > only to store NULL. So, ... OK. Actually, we should do the same optimization if a caller explicitly asks strvec_init_alloc(&array, 0); So perhaps we could do this if we wanted to encapsulate the tricky bits in a single place for maintainability. strvec.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git c/strvec.c w/strvec.c index f8de79f557..cbe72e9411 100644 --- c/strvec.c +++ w/strvec.c @@ -4,10 +4,21 @@ const char *empty_strvec[] = { NULL }; +void strvec_init_alloc(struct strvec *array, size_t alloc) +{ + if (!alloc) { + struct strvec blank = STRVEC_INIT; + memcpy(array, &blank, sizeof(*array)); + } else { + CALLOC_ARRAY(array->v, st_add(alloc, 1)); + array->nr = 0; + array->alloc = alloc + 1; + } +} + void strvec_init(struct strvec *array) { - struct strvec blank = STRVEC_INIT; - memcpy(array, &blank, sizeof(*array)); + strvec_init(array, 0); } void strvec_push_nodup(struct strvec *array, char *value)