Numpy `.view` function in C++

Question

I'm trying to convert a string into int32 in C++. In Python, I used to do:

import numpy as np
str = "HELLO"
np.array([str]).view(np.int32)

This results in:

array([72, 69, 76, 76, 79], dtype=int32)

i.e., the ord of each char.

How can I achieve the same in C++?

P. S. I'm not looking for Numpy-style way to accomplish this. But, looking for possible ways to obtain the same results.

To the downvoter, would you please post any comment regarding what is wrong with the question so that I can avoid in further questions. — Yassen Mehrez, Mar 31 '19 at 20:50
Possible duplicate of [NumPy style arrays for C++?](https://stackoverflow.com/questions/11169418/numpy-style-arrays-for-c) — zvone, Mar 31 '19 at 20:50
So, you just want to convert string to int? Use [atoi](http://www.cplusplus.com/reference/cstdlib/atoi/). BTW, also in Python I would not use numpy for that. I would just do `int(s)`. — zvone, Mar 31 '19 at 20:53
Man, have you really read the question. I'm aware of `atoi`, what it has to do with my question? — Yassen Mehrez, Mar 31 '19 at 20:56
True, I did not read everything :\ Ignore my comments. I added an answer. — zvone, Mar 31 '19 at 20:59

zvone · Answer 1 · 2019-03-31T22:24:58.870

0

In Python, this is what it does:

>>> import numpy as np
>>> str = "HELLO"
>>> np.array([str]).view(np.int32)
array([72, 69, 76, 76, 79])

In C/C++, "HELLO" already is the same thing as [72, 69, 76, 76, 79]!

static const char *s = "HELLO";
printf("%d\n", s[0]);   // prints 72
printf("%d\n", s[1]);   // prints 69
int x = s[2];   // x is now 76
printf("%d\n", x);   // prints 76

edited Mar 31 '19 at 22:24

answered Mar 31 '19 at 20:58

zvone

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The code you posted is erroneous. Also, this is the default `int`, I want `int32_t`. – Yassen Mehrez Mar 31 '19 at 21:06
@YassenHatem Eh, nit-picking does not really make a difference. Anyways, now the code is no longer erroneous. If you want `int32_t` instead of `int` just replace `int` with `int32_t` in the code. – zvone Mar 31 '19 at 22:26

score 0 · Accepted Answer · answered Apr 01 '19 at 12:48

0

You could do something like:

auto arr = new int32_t[str.length()];

Then use std::transform as:

std::transform(str.begin(), str.end(), arr, [](char chr) -> int32_t { return int32_t(chr); });

answered Apr 01 '19 at 12:48

ndrwnaguib

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Numpy `.view` function in C++

2 Answers2