Byte shifiting under msvc

Asked May 15 '15 at 18:18

Active May 15 '15 at 18:49

Viewed 71 times

I have a buffer where the first 4 bytes represents an unsigned 32bit integer. The buffer looks like this {32, 0, 0, 0, ...}

The following code works under gcc without any problems:

uint32_t size = buffer[0] | (buffer[1] << 8) | (buffer[2] << 16) | (buffer[3] << 24);

Size is 32 as expected but if i compile the project with msvc size is 538976288 instead of 32.

What is the problem?
EDIT: full source code for test:

#include <stdint.h>
#include <stdio.h>

int main()
{

    int pos = 0;
    uint32_t buffer [] = {32, 0, 0, 0};
    uint32_t size = buffer[pos++] | (buffer[pos++] << 8) | (buffer[pos++] << 16) | (buffer[pos++] << 24) ;
    printf("size=%d\n", size);
    return 0;
}

edited May 15 '15 at 18:49

houssam

1,823
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asked May 15 '15 at 18:18

NoFr1ends

538976288 is what you get if you put 32 in all four bytes, would there be any reason for that to happen? – harold May 15 '15 at 18:27
Only if it make a problem to use pos++ in the index of the array. e.g buffer[pos++] | (buffer[pos++] << 8) | (buffer[pos++] << 16) | (buffer[pos++] << 24) – NoFr1ends May 15 '15 at 18:29
Yes, that's a problem, don't do it – harold May 15 '15 at 18:31
Microsoft makes me laughing again... Thanks – NoFr1ends May 15 '15 at 18:32
Similar to http://stackoverflow.com/questions/949433/why-are-these-constructs-using-undefined-behavior – Igor Tandetnik May 15 '15 at 23:30

Byte shifiting under msvc

0 Answers0