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Let's get rid of sprintf() #101703

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Let's get rid of sprintf()#101703
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type-bugAn unexpected behavior, bug, or error

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@gvanrossum
gvanrossum
opened on Feb 8, 2023

On macOS with Xcode 14 we now get warnings like these:

Objects/unicodeobject.c:736:16: warning: 'sprintf' is deprecated: This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead. [-Wdeprecated-declarations]

While we can prove to ourselves that these specific sprintf() calls are safe, the warnings are annoying, but disabling them would also disable other, more useful warnings (or so @Yhg1s tells me on Discord). So let's just switch these to snprintf().

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  1. gvanrossum
    added
    type-bugAn unexpected behavior, bug, or error
    on Feb 8, 2023

  2. terryjreedy commented on Feb 8, 2023

    @terryjreedy
    terryjreedy
    on Feb 8, 2023
    Member

    There are 49 hits in our .c code + some in externals.

  3. sobolevn
    added 2 commits that reference this issue on Feb 9, 2023

    pythongh-101703: use `snprintf` instead of `sprintf`

    38f8e7d

    pythongh-101703: use `snprintf` instead of `sprintf`

    b33fb2d

  4. serhiy-storchaka commented on Feb 9, 2023

    @serhiy-storchaka
    serhiy-storchaka
    on Feb 9, 2023
    Member

    Interesting, there were issues with portability of snprintf (on Windows) in the past. I hope they were fixed in last 20 years.

  5. erlend-aasland commented on Feb 9, 2023

    @erlend-aasland
    erlend-aasland
    on Feb 9, 2023
    Contributor

    Interesting, there were issues with portability of snprintf (on Windows) in the past. I hope they were fixed in last 20 years.

    CC. @eryksun

  6. eryksun commented on Feb 9, 2023

    @eryksun
    eryksun
    on Feb 9, 2023
    Contributor

    Supported builds of Python 3.5+ on Windows use Visual Studio 2015+ and the Universal C Runtime (UCRT), for which snprintf() and vsnprintf() conform to C99. In Python 3.9+, "Include/pyerrors.h" no longer defines these two functions as macros that call non-standard _snprintf() and _vsnprintf().

    PyOS_vsnprintf() in "Python/mysnprintf.c" was apparently overlooked when "pyerrors.h" was updated. It should have been modified to always call vsnprintf(). Also, all PyOS_snprintf() and PyOS_vsnprintf() calls can be replaced with snprintf() and vsnprintf().

  7. terryjreedy commented on Apr 24, 2023

    @terryjreedy
    terryjreedy
    on Apr 24, 2023
    Member

    I closed #103733 as duplicate of this.

  8. gvanrossum commented on Mar 19, 2024

    @gvanrossum
    gvanrossum
    on Mar 19, 2024
    MemberAuthor

    @terryjreedy @sobolevn Can this be closed? I haven't seen those warnings in a while, though I see plenty of sprintf() calls in the code still.

  9. terryjreedy commented on Mar 20, 2024

    @terryjreedy
    terryjreedy
    on Mar 20, 2024
    Member

    I have no involvement with C code, so fine with me. @serhiy-storchaka ?

  10. sobolevn commented on Mar 20, 2024

    @sobolevn
    sobolevn
    on Mar 20, 2024
    Member

    I've tried to compile CPython with explicit -Wdeprecated-declarations set in PY_STDMODULE_CFLAGS and got no warnings. However, sprintf() is still widely used:

    » ag 'sprintf\('  
Misc/HISTORY
24555:  the standard sprintf() and vsprintf() C lib APIs, these versions
33626:similar to sprintf() in C.  The right argument is either a single
33627:value or a tuple of values.  All features of Standard C sprintf() are

Python/flowgraph.c
276:        sprintf(arg, "arg: %d ", i->i_oparg);
279:        sprintf(arg, "target: %p [%d] ", i->i_target, i->i_oparg);

Python/pystrtod.c
1204:        exp_len = sprintf(p, "%+.02d", exp);

Python/specialize.c
368:        sprintf(buf, "%s%s.txt", dirname, hex_name);

Objects/typeobject.c
5591:        sprintf(msg, "type_traverse() called on non-heap type '%.100s'",

Objects/unicodeobject.c
789:        size = sprintf(str, "&#%d;", PyUnicode_READ(kind, data, i));
2596:                    sprintf(buffer, fmt, va_arg(*vargs, long)) :
2597:                    sprintf(buffer, fmt, va_arg(*vargs, unsigned long));
2601:                    sprintf(buffer, fmt, va_arg(*vargs, long long)) :
2602:                    sprintf(buffer, fmt, va_arg(*vargs, unsigned long long));
2606:                    sprintf(buffer, fmt, va_arg(*vargs, Py_ssize_t)) :
2607:                    sprintf(buffer, fmt, va_arg(*vargs, size_t));
2610:                len = sprintf(buffer, fmt, va_arg(*vargs, ptrdiff_t));
2614:                    sprintf(buffer, fmt, va_arg(*vargs, intmax_t)) :
2615:                    sprintf(buffer, fmt, va_arg(*vargs, uintmax_t));
2619:                    sprintf(buffer, fmt, va_arg(*vargs, int)) :
2620:                    sprintf(buffer, fmt, va_arg(*vargs, unsigned int));
2672:        len = sprintf(number, "%p", va_arg(*vargs, void*));
8358:            sprintf(buffer, "&#%d;", (int)PyUnicode_READ_CHAR(unicode, collpos));

Objects/bytesobject.c
269:                sprintf(buffer, "%ld", va_arg(vargs, long));
272:                sprintf(buffer, "%zd", va_arg(vargs, Py_ssize_t));
275:                sprintf(buffer, "%d", va_arg(vargs, int));
283:                sprintf(buffer, "%lu", va_arg(vargs, unsigned long));
286:                sprintf(buffer, "%zu", va_arg(vargs, size_t));
289:                sprintf(buffer, "%u", va_arg(vargs, unsigned int));
296:            sprintf(buffer, "%i", va_arg(vargs, int));
302:            sprintf(buffer, "%x", va_arg(vargs, int));
328:            sprintf(buffer, "%p", va_arg(vargs, void*));
564:/* fmt%(v1,v2,...) is roughly equivalent to sprintf(fmt, v1, v2, ...) */

Parser/string_parser.c
134:                sprintf(p, "\\U%08x", chr);

Programs/_freeze_module.c
124:    sprintf(filename, "<frozen %s>", name);

Modules/_testexternalinspection.c
234:    sprintf(maps_file_path, "/proc/%d/maps", pid);

Modules/_pickle.c
2110:            sprintf(pdata, "%c%ld\n", INT,  val);

Modules/unicodedata.c
1329:        sprintf(buffer, "CJK UNIFIED IDEOGRAPH-%X", code);

Modules/_testcapimodule.c
991:        sprintf(buffer, "%s module: \"%s\" attribute: \"%s\"", \

Modules/getnameinfo.c
142:        sprintf(numserv, "%d", ntohs(port));

Modules/_datetimemodule.c
1629:        sprintf(freplacement, "%06d", TIME_GET_MICROSECOND(object));
1631:        sprintf(freplacement, "%06d", DATE_GET_MICROSECOND(object));
1633:        sprintf(freplacement, "%06d", 0);

Modules/_ctypes/stgdict.c
651:            sprintf(buf, "%s:%s:", fieldfmt, fieldname);

Modules/_ctypes/_ctypes.c
398:                sprintf(buf, "%zd,", shape[k]);
400:                sprintf(buf, "%zd)", shape[k]);
2538:    cp += sprintf(cp, "%x", Py_SAFE_DOWNCAST(index, Py_ssize_t, int));
2547:        cp += sprintf(cp, ":%x", Py_SAFE_DOWNCAST(target->b_index, Py_ssize_t, int));
3269:        sprintf(mangled_name, "_%s@%d", name, i*4);
4768:    sprintf(name, "%.200s_Array_%Id",
4771:    sprintf(name, "%.200s_Array_%ld",

    Not sure why this warning is gone.

  11. erlend-aasland commented on Mar 20, 2024

    @erlend-aasland
    erlend-aasland
    on Mar 20, 2024
    Contributor

    Well, we risk that when the next version your toolchain of choice is updated, the warnings will reappear. IMO we might as well fix them. @sobolevn's PR was a good start, but only needed to be split in more manageable chunks.

  12. sobolevn commented on Mar 20, 2024

    @sobolevn
    sobolevn
    on Mar 20, 2024
    Member

    I can redo some parts of it, there were rather easy. I'll start with them today.

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