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perlclib - Internal replacements for standard C library functions


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.


In the following tables:


is a type.


is a pointer.


is a number.


is 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) (Dep-
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(p, n, t)
t* p = calloc(n, s)            Newxz(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(dst, src, sizeof(t))    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

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)

memcmp(p1, p2, n)              memNE(p1, p2, n)
!memcmp(p1, p2, n)             memEQ(p1, p2, 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() macros, which have similar arguments to Zero():

PoisonWith(dst, n, t, b)    scribble memory with byte b
PoisonNew(dst, n, t)        equal to PoisonWith(dst, n, t, 0xAB)
PoisonFree(dst, n, t)       equal to PoisonWith(dst, n, t, 0xEF)
Poison(dst, n, t)           equal to PoisonFree(dst, n, t)

Character Class Tests

There are several types of character class tests that Perl implements. The only ones described here are those that directly correspond to C library functions that operate on 8-bit characters, but there are equivalents that operate on wide characters, and UTF-8 encoded strings. All are more fully described in "Character classification" in perlapi and "Character case changing" in perlapi.

The C library routines listed in the table below return values based on the current locale. Use the entries in the final column for that functionality. The other two columns always assume a POSIX (or C) locale. The entries in the ASCII column are only meaningful for ASCII inputs, returning FALSE for anything else. Use these only when you know that is what you want. The entries in the Latin1 column assume that the non-ASCII 8-bit characters are as Unicode defines, them, the same as ISO-8859-1, often called Latin 1.

Instead Of:  Use for ASCII:   Use for Latin1:      Use for locale:

isalpha(c)  isALPHA(c)        isALPHA_L1(c)        isALPHA_LC(u )
isascii(c)  isASCII(c)                             isASCII_LC(c)
isblank(c)  isBLANK(c)        isBLANK_L1(c)        isBLANK_LC(c)
iscntrl(c)  isCNTRL(c)        isCNTRL_L1(c)        isCNTRL_LC(c)
isdigit(c)  isDIGIT(c)        isDIGIT_L1(c)        isDIGIT_LC(c)
isgraph(c)  isGRAPH(c)        isGRAPH_L1(c)        isGRAPH_LC(c)
islower(c)  isLOWER(c)        isLOWER_L1(c)        isLOWER_LC(c)
isprint(c)  isPRINT(c)        isPRINT_L1(c)        isPRINT_LC(c)
ispunct(c)  isPUNCT(c)        isPUNCT_L1(c)        isPUNCT_LC(c)
isspace(c)  isSPACE(c)        isSPACE_L1(c)        isSPACE_LC(c)
isupper(c)  isUPPER(c)        isUPPER_L1(c)        isUPPER_LC(c)
isxdigit(c) isXDIGIT(c)       isXDIGIT_L1(c)       isXDIGIT_LC(c)

tolower(c)  toLOWER(c)        toLOWER_L1(c)        toLOWER_LC(c)
toupper(c)  toUPPER(c)                             toUPPER_LC(c)

To emphasize that you are operating only on ASCII characters, you can append _A to each of the macros in the ASCII column: isALPHA_A, isDIGIT_A, and so on.

(There is no entry in the Latin1 column for isascii even though there is an isASCII_L1, which is identical to isASCII; the latter name is clearer. There is no entry in the Latin1 column for toupper because the result can be non-Latin1. You have to use toUPPER_uni, as described in "Character case changing" in perlapi.)

stdlib.h functions

Instead Of:                 Use:

atof(s)                     Atof(s)
atoi(s)                     grok_atoUV(s, &uv, &e)
atol(s)                     grok_atoUV(s, &uv, &e)
strtod(s, &p)               Nothing.  Just don't use it.
strtol(s, &p, n)            grok_atoUV(s, &uv, &e)
strtoul(s, &p, n)           grok_atoUV(s, &uv, &e)

Typical use is to do range checks on uv before casting:

int i; UV uv; char* end_ptr;
if (grok_atoUV(input, &uv, &end_ptr)
    && uv <= INT_MAX)
  i = (int)uv;
  ... /* continue parsing from end_ptr */
} else {
  ... /* parse error: not a decimal integer in range 0 .. MAX_IV */

Notice also the grok_bin, grok_hex, and grok_oct functions in numeric.c for converting strings representing numbers in the respective bases into NVs. Note that grok_atoUV() doesn't handle negative inputs, or leading whitespace (being purposefully strict).

Note that strtol() and strtoul() may be disguised as Strtol(), Strtoul(), Atol(), Atoul(). Avoid those, too.

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_setenv(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).


perlapi, perlapio, perlguts