in reply to What difference between malloc and Newx, how attach a C string to SV directly?

Hi,

The reason you get a segmentation fault is because when ddd() ends char* dx gets freed

I think the idea is to use SvPV to get a char* to give to your C function, something like this but by a real c-programmer :)

I couldn't get it to compile using SvPV or SvPVX calls, dont understand why , error is

error: lvalue required as left operand of assignment
error: lvalue required as unary '&' operand

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This compiles but I couldn't make this assign ddddd string , needs c-programmer 

#!/usr/bin/perl --
use strict;
use warnings;
use Inline C => Config => BUILD_NOISY => 1, CLEAN_AFTER_BUILD => 0;
use Inline 'C' => <<'CODE',  NAME =>  'xiaoyafeng';

int ddd(SV* x){
    SvUTF8_off(x);
    SvGROW(x,10);
    char*buff = SvPV_nolen(x);
    *buff = "dddddd\n";
    printf("SV* x is %p \n", x);
    printf("SvPV(x) is %p \n", SvPV_nolen(x));
    printf("string buff is %p \n", buff);
    SvCUR_set(x, 10);
    SvSETMAGIC(x);
    return 0;
}
CODE



use Devel::Peek qw/ Dump /;
my $x = "";
Dump $x;
ddd($x);
Dump $x;
exit( 0 );

__END__
SV = PV(0x3f7a8c) at 0x99bca4
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0xf46a04 ""\0
  CUR = 0
  LEN = 12
SV* x is 0099BCA4
SvPV(x) is 00F46A04
string buff is 00F46A04
SV = PV(0x3f7a8c) at 0x99bca4
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0xf46a04 "$\0matched\0"
  CUR = 10
  LEN = 12

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Re^2: What difference between malloc and Newx, how attach a C string to SV directly?
by Anonymous Monk on Sep 29, 2019 at 09:11 UTC 
    #!/usr/bin/perl --
use strict;
use warnings;
use Inline C => Config => BUILD_NOISY => 1, CLEAN_AFTER_BUILD => 0;
use Inline 'C' => <<'CODE',  NAME =>  'xiaoyafeng';
int ddd(SV* x){
    printf("SV* x is %p \n", x);
    SvUTF8_off(x);
    SvGROW(x,8);
    SvCUR_set(x, 8);
    printf("SvPV(x) is p(%p) \n", SvPV_nolen(x));
    printf("SvPV(x) is s(%s) \n", SvPV_nolen(x));
    char*buff = SvPV_nolen(x);
    Copy( "dddddddd", buff , 8, char);
    printf("SvPV(x) is p(%p) \n", SvPV_nolen(x));
    printf("SvPV(x) is s(%s) \n", SvPV_nolen(x));
    printf("string buff is p(%p) \n", buff);
    printf("string buff is s(%s) \n", buff);
    SvSETMAGIC(x);
    return 0;
}
CODE



use Devel::Peek qw/ Dump /;
my $x = "";
Dump $x;
ddd($x);
Dump $x;
exit( 0 );

__END__
SV = PV(0x3f7a8c) at 0x99bca4
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0xb2ac54 ""\0
  CUR = 0
  LEN = 12
SV* x is 0099BCA4
SvPV(x) is p(00B2AC54)
SvPV(x) is s()
SvPV(x) is p(00B2AC54)
SvPV(x) is s(ddddddddng)
string buff is p(00B2AC54)
string buff is s(ddddddddng)
SV = PV(0x3f7a8c) at 0x99bca4
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0xb2ac54 "dddddddd"
  CUR = 8
  LEN = 12

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