c - Struct causing sysMalloc assertion to fail and double free() errors -

i writing simple struct called process, , code seems implemented correctly @ quick glance, upon testing code seems keep crashing program, either sysmalloc assertion failure or double free() error when 1 attempts free it.

some relevant code:

declaration

typedef struct process{     int pid;     int background;     int group;     int status;     char* name = 0; } process; 

constructor

process* process_init(char* name, int pid, int group, int background){     process* output    = (process*)calloc(1, sizeof(process*));     output->name       = name;     output->pid        = pid;     output->group      = group;     output->background = background;     output->status     = 0;      return output; } 

calling code

char* command = "python"; char* command1= "cat < testing";  process* proc = process_init("command", 1, 1, 1); process* proc2 = process_init("command1", 1, 1, 1); 

there weird behavior appears work first time around, causes sysmalloc error when called second time (which why call twice.)

i tried using valgrind , gave me following:

invalid write of size 4 ==3485==    @ 0x8049a03: process_init (process.c:6) ==3485==    0x80488c2: main (test.c:58) ==3485==  address 0x419e730 12 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488c2: main (test.c:58) ==3485==  ==3485== invalid write of size 4 ==3485==    @ 0x8049a14: process_init (process.c:8) ==3485==    0x80488c2: main (test.c:58) ==3485==  address 0x419e728 4 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488c2: main (test.c:58) ==3485==  ==3485== invalid write of size 4 ==3485==    @ 0x8049a1d: process_init (process.c:9) ==3485==    0x80488c2: main (test.c:58) ==3485==  address 0x419e724 0 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488c2: main (test.c:58) ==3485==  ==3485== invalid write of size 4 ==3485==    @ 0x8049a23: process_init (process.c:10) ==3485==    0x80488c2: main (test.c:58) ==3485==  address 0x419e72c 8 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488c2: main (test.c:58) ==3485==  ==3485== invalid write of size 4 ==3485==    @ 0x8049a03: process_init (process.c:6) ==3485==    0x80488ea: main (test.c:59) ==3485==  address 0x419e768 12 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488ea: main (test.c:59) ==3485==  ==3485== invalid write of size 4 ==3485==    @ 0x8049a14: process_init (process.c:8) ==3485==    0x80488ea: main (test.c:59) ==3485==  address 0x419e760 4 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488ea: main (test.c:59) ==3485==  ==3485== invalid write of size 4 ==3485==    @ 0x8049a1d: process_init (process.c:9) ==3485==    0x80488ea: main (test.c:59) ==3485==  address 0x419e75c 0 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488ea: main (test.c:59) ==3485==  ==3485== invalid write of size 4 ==3485==    @ 0x8049a23: process_init (process.c:10) ==3485==    0x80488ea: main (test.c:59) ==3485==  address 0x419e764 8 bytes after block of size 4 alloc'd ==3485==    @ 0x402425f: calloc (vg_replace_malloc.c:467) ==3485==    0x80499f9: process_init (process.c:5) ==3485==    0x80488ea: main (test.c:59) --snip-- 

so, looks problem in constructor, i'm not sure why since looks straightforward moving around of variables.

process* output    = (process*)calloc(1, sizeof(process*)); 

this incorrect. you're allocating enough memory pointer (4 or 8 bytes).

the proper code:

process* output    = calloc(1, sizeof(*output)); 

improvements:

1. it's correct! allocating enough bytes whatever output points to, process, instead of enough bytes pointer process.
2. by saying sizeof(*output), remove additional reference type name (dry), ensures code correct, if changes type output points to, , forgets change rest of line.
3. i've removed cast result of calloc. calloc returns void* can assigned pointer type variable without cast.

also, should checking return value of function, 1 returns memory:

process* process_init(char* name, int pid, int group, int background){     process* output    = calloc(1, sizeof(*output));     if (output == null)         return null;      output->name       = name;     output->pid        = pid;     output->group      = group;     output->background = background;     output->status     = 0;      return output; } 

any consumer of function should check return value well.