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
– Yassen Mehrez, Commented Mar 31, 2019 at 20:50
So, you just want to convert string to int? Use atoi. BTW, also in Python I would not use numpy for that. I would just do int(s). — zvone
– zvone, Commented Mar 31, 2019 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
– Yassen Mehrez, Commented Mar 31, 2019 at 20:56

ndrwnaguib · Accepted Answer · 2019-04-01 12:48:16Z

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 1, 2019 at 12:48

ndrwnaguib

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zvone · Accepted Answer · 2019-03-31 22:24:58Z

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, 2019 at 22:24

answered Mar 31, 2019 at 20:58

zvone

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2 Comments

Yassen Mehrez Over a year ago

The code you posted is erroneous. Also, this is the default int, I want int32_t.

zvone Over a year ago

@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.

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