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[英]C++: How to read specific number of bytes from a binary file and save it to uint16_t?
[英]Read binary file and count specific number c++
嘿,我一直在到处寻找有关如何执行此特定任务的见解。 我看到了类似的内容,但没有明确的解释。 我正在尝试读取bin文件并计算特定数字出现的次数。 我看到了使用.txt文件的示例,并且使用getline看起来非常简单。 我试图复制类似的结构,但使用二进制文件。
int main() {
int searching = 3;
int counter = 0;
unsigned char * memblock;
long long int size;
//open bin file
ifstream file;
file.open("threesData.bin", ios:: in | ios::binary | ios::ate);
//read bin file
if (file.is_open()) {
cout << "it opened\n";
size = file.tellg();
memblock = new unsigned char[size];
file.seekg(0, ios::beg);
file.read((char * ) memblock, size);
while (file.read((char * ) memblock, size)) {
for (int i = 0; i < size; i++) {
(int) memblock[i];
if (memblock[i] == searching) {
counter++;
}
}
}
}
file.close();
cout << "The number " << searching << " appears ";
cout << counter << " times!";
return 0;
}
当我运行该程序时,很明显它会打开,但不计算我要搜索的数字。 我究竟做错了什么?
您似乎一直在考虑这个问题,但是这就是我要做的事情。
array[size_t]
语法进行更简单的运算。 码
#include <fstream>
#include <iostream>
bool check_character(int value)
{
return value == 3;
}
int main(void)
{
// choose the size, cast a pointer as an int type, and initialize
// our counter
static constexpr size_t size = 4096;
char* buffer = new char[size];
int* ints = (int*) buffer;
size_t counter = 0;
// create our stream,
std::ifstream stream("file.bin", std::ios_base::binary);
while (stream) {
// keep reading while the stream is valid
stream.read(buffer, size);
auto count = stream.gcount();
// we only want to go to the last valid integer
// if we expect the file to be only integers,
// we could do `assert(count % sizeof(int) == 0);
// otherwise, we may have trailing characters
// if we have trailing characters, we may want to move them
// to the front of the buffer....
auto chars = count / sizeof(int); // floor division
for (size_t i = 0; i < chars; ++i) {
// false == 0, true == 1, so we can just add
// if the value is 3
counter += check_character(ints[i]);
}
}
std::cout << "Counter is: " << counter << std::endl;
delete[] buffer;
return 0;
}
正如NeilButterworth指出的那样,您也可以使用向量。 我不是很喜欢这个,但是“嗯”。
#include <fstream>
#include <iostream>
#include <vector>
/* ellipsed lines */
int main(void)
{
/* ellipsed lines */
static constexpr size_t size = 4096;
std::vector<int> ints;
ints.resize(size / sizeof(int));
char* buffer = (char*) ints.data();
/* ellipsed lines */
/* ellipsed lines */
std::cout << "Counter is: " << counter << std::endl;
// no delete[]
return 0;
}
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