如何在矢量矢量的開始處添加新行

Question

我想在矢量矢量的開始處添加新行。我有一個3x3矢量，我想要一個4x3。這是我的代碼：

typedef vector<int> state; 
typedef vector<vector<int> > board; 

int val; 
string s; 

while (getline (in, s)) { 
    istringstream iss (s); 

    while (iss >> val) 
     boards.push_back(val); 
} 

sizeb = boards.front(); 

for (auto it = boards.cbegin()+1; it <= boards.cbegin()+pow(sizeb, 2); ++it) 
    sstart.push_back(*it); 

start.resize(sizeb); 

for (int i = 0; i < sizeb; ++i) 
    start[i].resize(sizeb); 

for (int i = 0; i < sizeb; i++) 
    for (int j = 0; j < sizeb; j++) 
     start[i][j] = sstart[(i * sizeb) + j]; 

當我嘗試做sizeb + 1時，它會添加一個新行，但也會添加一個新列。

你能幫我嗎？

Answer 1

How to add a new row at the begin of a vector of vectors

你可以用std::vector::insert來做到這一點。

When I try to do sizeb+1 it adds a new row but also a new column.

那是因爲你使用循環調整的每一行：

// I'm assuming that start is the vector of vectors 

start.resize(sizeb); // this changes the number of rows 

for (int i = 0; i < sizeb; ++i) 
    start[i].resize(sizeb); // these change the number of columns in each row