NAME
perlclib - Internal replacements for standard C library functions
DESCRIPTION
One thing Perl porters should note is that perl doesn't tend to use that much of the C standard library internally; you'll see very little use of, for example, the ctype.h functions in there. This is because Perl tends to reimplement or abstract standard library functions, so that we know exactly how they're going to operate.
This is a reference card for people who are familiar with the C library and who want to do things the Perl way; to tell them which functions they ought to use instead of the more normal C functions.
Conventions
In the following tables:
tis a type.
pis a pointer.
nis a number.
sis a string.
sv
, av
, hv
, etc. represent variables of their respective types.
File Operations
Instead of the stdio.h functions, you should use the Perl abstraction
layer. Instead of FILE*
types, you need to be handling PerlIO*
types. Don't forget that with the new PerlIO layered I/O abstraction
FILE*
types may not even be available. See also the perlapio
documentation for more information about the following functions:
Instead Of: Use:
stdin PerlIO_stdin()
stdout PerlIO_stdout()
stderr PerlIO_stderr() fopen(fn, mode) PerlIO_open(fn, mode)
freopen(fn, mode, stream) PerlIO_reopen(fn, mode, perlio) (Deprecated)
fflush(stream) PerlIO_flush(perlio)
fclose(stream) PerlIO_close(perlio)File Input and Output
Instead Of: Use:
fprintf(stream, fmt, ...) PerlIO_printf(perlio, fmt, ...)
[f]getc(stream) PerlIO_getc(perlio)
[f]putc(stream, n) PerlIO_putc(perlio, n)
ungetc(n, stream) PerlIO_ungetc(perlio, n)Note that the PerlIO equivalents of fread
and fwrite
are slightly
different from their C library counterparts:
fread(p, size, n, stream) PerlIO_read(perlio, buf, numbytes)
fwrite(p, size, n, stream) PerlIO_write(perlio, buf, numbytes)fputs(s, stream) PerlIO_puts(perlio, s)
There is no equivalent to fgets
; one should use sv_gets
instead:
fgets(s, n, stream) sv_gets(sv, perlio, append)
File Positioning
Instead Of: Use:
feof(stream) PerlIO_eof(perlio)
fseek(stream, n, whence) PerlIO_seek(perlio, n, whence)
rewind(stream) PerlIO_rewind(perlio) fgetpos(stream, p) PerlIO_getpos(perlio, sv)
fsetpos(stream, p) PerlIO_setpos(perlio, sv) ferror(stream) PerlIO_error(perlio)
clearerr(stream) PerlIO_clearerr(perlio)Memory Management and String Handling
Instead Of: Use:
t* p = malloc(n) Newx(id, p, n, t)
t* p = calloc(n, s) Newxz(id, p, n, t)
p = realloc(p, n) Renew(p, n, t)
memcpy(dst, src, n) Copy(src, dst, n, t)
memmove(dst, src, n) Move(src, dst, n, t)
memcpy/*(struct foo *) StructCopy(src, dst, t)
memset(dst, 0, n * sizeof(t)) Zero(dst, n, t)
memzero(dst, 0) Zero(dst, n, char)
free(p) Safefree(p) strdup(p) savepv(p)
strndup(p, n) savepvn(p, n) (Hey, strndup doesn't exist!) strstr(big, little) instr(big, little)
strcmp(s1, s2) strLE(s1, s2) / strEQ(s1, s2) / strGT(s1,s2)
strncmp(s1, s2, n) strnNE(s1, s2, n) / strnEQ(s1, s2, n)Notice the different order of arguments to Copy
and Move
than used
in memcpy
and memmove
.
Most of the time, though, you'll want to be dealing with SVs internally
instead of raw char *
strings:
strlen(s) sv_len(sv)
strcpy(dt, src) sv_setpv(sv, s)
strncpy(dt, src, n) sv_setpvn(sv, s, n)
strcat(dt, src) sv_catpv(sv, s)
strncat(dt, src) sv_catpvn(sv, s)
sprintf(s, fmt, ...) sv_setpvf(sv, fmt, ...)Note also the existence of sv_catpvf
and sv_vcatpvfn
, combining
concatenation with formatting.
Sometimes instead of zeroing the allocated heap by using Newxz() you should consider "poisoning" the data. This means writing a bit pattern into it that should be illegal as pointers (and floating point numbers), and also hopefully surprising enough as integers, so that any code attempting to use the data without forethought will break sooner rather than later. Poisoning can be done using the Poison() macro, which has similar arguments as Zero():
Poison(dst, n, t)
Character Class Tests
There are two types of character class tests that Perl implements: one
type deals in char
s and are thus not Unicode aware (and hence
deprecated unless you know you should use them) and the other type
deal in UV
s and know about Unicode properties. In the following
table, c
is a char
, and u
is a Unicode codepoint.
Instead Of: Use: But better use:
isalnum(c) isALNUM(c) isALNUM_uni(u)
isalpha(c) isALPHA(c) isALPHA_uni(u)
iscntrl(c) isCNTRL(c) isCNTRL_uni(u)
isdigit(c) isDIGIT(c) isDIGIT_uni(u)
isgraph(c) isGRAPH(c) isGRAPH_uni(u)
islower(c) isLOWER(c) isLOWER_uni(u)
isprint(c) isPRINT(c) isPRINT_uni(u)
ispunct(c) isPUNCT(c) isPUNCT_uni(u)
isspace(c) isSPACE(c) isSPACE_uni(u)
isupper(c) isUPPER(c) isUPPER_uni(u)
isxdigit(c) isXDIGIT(c) isXDIGIT_uni(u) tolower(c) toLOWER(c) toLOWER_uni(u)
toupper(c) toUPPER(c) toUPPER_uni(u)stdlib.h functions
Instead Of: Use:
atof(s) Atof(s)
atol(s) Atol(s)
strtod(s, *p) Nothing. Just don't use it.
strtol(s, *p, n) Strtol(s, *p, n)
strtoul(s, *p, n) Strtoul(s, *p, n)Notice also the grok_bin
, grok_hex
, and grok_oct
functions in
numeric.c for converting strings representing numbers in the respective
bases into NV
s.
In theory Strtol
and Strtoul
may not be defined if the machine perl is
built on doesn't actually have strtol and strtoul. But as those 2
functions are part of the 1989 ANSI C spec we suspect you'll find them
everywhere by now.
int rand() double Drand01()
srand(n) { seedDrand01((Rand_seed_t)n);
PL_srand_called = TRUE; } exit(n) my_exit(n)
system(s) Don't. Look at pp_system or use my_popen getenv(s) PerlEnv_getenv(s)
setenv(s, val) my_putenv(s, val)Miscellaneous functions
You should not even want to use setjmp.h functions, but if you
think you do, use the JMPENV
stack in scope.h instead.
For signal
/sigaction
, use rsignal(signo, handler)
.
SEE ALSO
perlapi
, perlapio
, perlguts
