use prev pointer when array do adding

[xiaomianhehe]

The array do add_item was slow, use prev pointer to avoid while loop

[Alanscut]

shouldn't the prev of item be NULL? and the default value of item's prev and next item is NULL, so there is no need to point it, what do you think?

[xiaomianhehe]

if the object is array, we could use the prev pointer, so we can do array_add more quick by "prev".
we don't need to find the last item one by one

[xiaomianhehe]

if the size of array is large , we could do array_add better

[Alanscut]

oh, I just catch your idea, prev way is indeed faster for large array.

[xiaomianhehe]

yayaya, i use it in my project, the performance improve about 30 percent when create a cjson array which has thousand's item.
it could be better, if the element is easier.

[Alanscut]

why not add the _ prefix? I prefer to use index over _index, index is more in line with the naming convention of cJSON

[xiaomianhehe]

while compile, it promt the index was a function in string.h
so use _index would be better?

[Alanscut]

what's your compiler? I have never met this before...

[xiaomianhehe]

gcc-4.4.7 centios6.5.
we include the string.h file ,and it has a function namd "index",we could modify the compile option, and ignore it, but i don't think it is a good idea

[xiaomianhehe]

i use same compile option,such as Werror, Wall, in my project.

[xiaomianhehe]

there are two different c standard. cmakelist.txt configured the option "-std=c89" ,but i use std=gnu99.
I modifid the "std=c89" option to "std=gnu99" in the cmakelist.txt, and it reproduced.

[Alanscut]

@xiaomianhehe I have modified the std to gnu99, but still no warning. I tested it in macOS, centOS(7.2, gcc4.8.5) and ubuntu(18.04, gcc 7.4.0).
only when string.h has a global varialble named index, the prompt will show.
Have you changed the file of /usr/include/string.h? make sure there is no redundant global variable of index.

• dup_name.c

#include <stdio.h>
#include <string.h>
#include "lib1.h" // when including lib1.h, it failed.

void func(int index) {
    printf("index = %d\n", index);
}

int main() {
    func(5); // print: index = 5
    char *str = "hello world";
    char *res = index(str, 'o');
    printf("%s\n", res);   // print: o world
    return 0;
}

• lib1.h

int index = 0;

As far as I know, method parameter of local variable named index is very common. such as jsoncpp, you could try to compile it and above example code.

After this issue is resolved, I will merge your PR.

[xiaomianhehe]

You are right. i try gcc-4.4.7(Centos6.5)and gcc-4.8.5(centos7.2), the result was different.
it has warning with gcc-4.4.7.

[Alanscut]

so I think there is no need to change index, do you agree?

[xiaomianhehe]

Ok, I revert it.I modify it in my project, because we use old version gcc and centos in our produce env.

[Alanscut]

please revert _index to index

[xiaomianhehe]

Done.

[Alanscut]

Thanks!