[英]Reading data from a file and storing each line in an array?
I have a file with lines of integers. 我有一个整数行的文件。 I want to read each line into a slot in my array.
我想将每一行读入我的数组中的一个插槽。 I have the code below, but it does not work.
我有下面的代码,但它不起作用。 I'm not sure if I'm on the right track.
我不确定我是否走在正确的轨道上。
void Read_Save() {
ifstream in;
int arr[100];
string line;
in.open("file.txt");
while (in.peek() != EOF)
{
getline(in, line, '\n');
strcpy(arr, line.c_str());
}
in.clear(); in.close();
}
There are several ways to parse the integer value out of the string. 有几种方法可以解析字符串中的整数值。
First, let's fix your loop: 首先,让我们修复你的循环:
int pos = 0;
while( std::getline(in, line) && pos < 100 )
{
int value = 0;
// Insert chosen parsing method here
arr[pos++] = value;
}
Here is a non-exhaustive list of common options: 以下是常见选项的非详尽列表:
Use std::strtol
使用
std::strtol
// Will return 0 on error (indistinguishable from parsing actual 0) value = std::strtol( line.c_str(), nullptr, 10 );
// Will throw exception on error value = std::stoi( line );
Build a std::istringstream
and read from it: 构建一个
std::istringstream
并从中读取:
std::istringstream iss( line ); iss >> value; if( !iss ) { // Failed to parse value. }
Use std::sscanf
使用
std::sscanf
if( 1 != std::sscanf( line.c_str(), "%d", &value ) ) { // Failed to parse value. }
Now, note the bounds-test on the loop checking pos < 100
. 现在,注意循环检查
pos < 100
的边界测试。 This is because your array has a storage limit. 这是因为您的阵列具有存储限制。 Actually, you have also overridden the global one with a local one in
Read_Save
, thus hiding it with a smaller array that will be lost when the function finishes. 实际上,你还使用
Read_Save
的本地数据覆盖了全局的Read_Save
,从而将它隐藏在一个较小的数组中,该数组在函数完成时将丢失。
You can have an arbitrary-sized "array" (not actually an array) using other container types provided by the standard library. 您可以使用标准库提供的其他容器类型来拥有任意大小的“数组”(实际上不是数组)。 Useful ones that provide random access are
std::vector
and std::deque
. 提供随机访问的有用的是
std::vector
和std::deque
。 Let's use the vector and change the definition of Read_Save
to be a bit more useful: 让我们使用向量并将
Read_Save
的定义更改为更有用:
std::vector<int> Read_Save( std::istream & in )
{
std::vector<int> values;
std::string line;
for( int line_number = 1; getline( in, line ); line_number++ )
{
try {
int value = std::stoi( line );
values.push_back( value );
}
catch( std::bad_alloc & e )
{
std::cerr << "Error (line " << line_number << "): Out of memory!" << std::endl;
throw e;
}
catch( std::exception & e)
{
std::cerr << "Error (line " << line_number << "): " << e.what() << std::endl;
}
}
return values;
}
And finally, the call becomes: 最后,电话变为:
std::ifstream in( "file.txt" );
std::vector<int> values = Read_Save( in );
You cannot use strcpy()
to convert a string to an integer. 您不能使用
strcpy()
将字符串转换为整数。 You can use std::strtol()
or std::stoi()
, or even a std::istringstream
, eg: 你可以使用
std::strtol()
或std::stoi()
,甚至是std::istringstream
,例如:
int arr[1000];
void Read_Save() {
ifstream in;
string line;
in.open("file.txt");
int index = 0;
while ((index < 1000) && (getline(in, line)))
{
if (istringstream(line) >> arr[index])
++index;
}
}
The best thing to do in your case is to use std::vector
. 在你的情况下,最好的办法是使用
std::vector
。 The code would look like this: 代码如下所示:
void Read_Save()
{
std::ifstream in("file.txt");
int value;
std::vector<int> arr;
while (in >> value)
arr.push_back(value);
for(int i(0); i < arr.size(); i++)
std::cout << arr[i] << ", ";
std::cout << std::endl;
in.close();
}
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