c++ - Qt QVector allocation via resize() results in bad_alloc where reserve() seems to work -

so want allocate 1gb of data in qvector. far use this:

void foo (float* data, size_t size) {     qvector<float> resultvec;     resultvec.resize(size);      //i stuff on vector      size_t paddinglength = nextpow2(size); //calculates next highest power 2 two      //the paddinglength in case @ moment: 268.435.456     // results in bad_alloc     resultvec.resize(paddinglength);   } 

so in case of floats want reserve 1gb worth of space. should not problem @ all. still have 11gb on ram left. tried @ point in program , works fine, sizes in order of 4gb.

my first guess don't have enough continuous space left, when try same reserving space before resizing it, works.

void foo (float* data, size_t size) {     qvector<float> resultvec;     resultvec.resize(size);      //i stuff on vector      size_t paddinglength = nextpow2(size); //calculates next highest power 2 two      //the paddinglength in case @ moment: 268.435.456     //this works tho     resultvec.reserve(paddinglength);     resultvec.resize(paddinglength);   }  template<typename t> t nextpow2 (const t val) {     t result = val;      (size_t = 1; < sizeof(t) * char_bit; *= 2)     {         result |= result >> i;     }     return result + 1; } 

fyi: did check return value of next2pow , sure smaller limit of int. shown in comments value bit on 268 million elements, int has maximum of on 2 billion, should safe there. included next2pow implementation above.

am doing wrong, or behaviour expected?