将C ++向量写入输出文件

Question

ofstream outputFile ("output.txt");

if (outputFile.is_open())
{
     outputFile << "GLfloat vector[]={" <<  copy(vector.begin(), vector.end(), ostream_iterator<float>(cout, ", ")); << "}" << endl;
}
else cout << "Unable to open output file";

How do I output a vector to a file, with each float separated by commas? I would also like to avoid printing square brackets if possible.

Answer 1

outputFile << "GLfloat vector[]={";
copy(vector.begin(), vector.end(), ostream_iterator<float>(outputFile , ", ")); 
                                                           ^^^^^^^^^^
outputFile << "}" << endl;

Answer 2

First, you shouldn't call your variable vector . Give it a name which is not the name of a class from the Standard Library.

Secondly, ostream_iterator will append a ',' even after the last element of the vector, which may not be what you want (a separator should be a separator , and there's nothing to separate the last value of the vector from a further value).

In C++11, you could use a simple range-based for loop:

outputFile << "GLfloat vector[]={";
auto first = true;
for (float f : v) 
{ 
    if (!first) { outputFile << ","; } 
    first = false; 
    outputFile << f; 
}
outputFile << "}" << endl;

In C++03, it is going to be just a bit more verbose:

outputFile << "GLfloat vector[]={";
auto first = true;
for (vector<float>::iterator i = v.begin(); i != end(); ++i) 
{ 
    if (!first) { outputFile << ","; c++; } 
    first = false;
    outputFile << *i;
}
outputFile << "}" << endl;

Answer 3

You've taken the solution and attempted to stick it into the stream insertion. That's not how it works. It should be a separate line:

outputFile << "GLfloat vector[]={";
copy(vector.begin(), vector.end(), ostream_iterator<float>(outputFile, ", "));
outputFile << "}" << endl;

The copy algorithm simply copies elements from one range to another. ostream_iterator is a special iterator that will actually insert (with << ) into the given stream when you do *it = item_to_insert; .

Answer 4

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