Question

C# coder just wrote this simple C++ method to get text from a file:

static std::vector<std::string> readTextFile(const std::string &filePath) {
    std::string line;
    std::vector<std::string> lines;
    std::ifstream theFile(filePath.c_str());
    while (theFile.good()) {
    getline (theFile, line);
        lines.push_back(line);
    }
    theFile.close();
    return lines;
}   

I know this code is not efficient; the text lines are copied once as they are read and a second time when returned-by-value.

Two questions:

(1) can this code leak memory ?
(2) more generally can returning containers of objects by value ever leak memory ? (assuming the objects themselves don’t leak)

Answer 1

while (theFile.good()) {
 getline (theFile, line);
    lines.push_back(line);
}

Forget about efficiency, this code is not correct. It will not read the file correctly. See the following topic to know why:

• What's preferred pattern for reading lines from a file in C++?

So the loop should be written as:

while (getline (theFile, line)) {
    lines.push_back(line);
}

Now this is correct. If you want to make it efficient, profile your application first. Try see the part which takes most CPU cycles.

---

(1) can this code leak memory ?

No.

(2) more generally can returning containers of objects by value ever leak memory ?

Depends on the type of the object in the containers. In your case, the type of the object in std::vector is std::string which makes sure that no memory will be leaked.