打印出表的列名

Question

我現在有這個功能，打印出我的表的每一行

static int callback(void *NotUsed, int argc, char **argv, char **szColName) 
{ 
    for(int i = 0; i < argc; i++) 
    { 
     cout.width(17); cout << left << argv[i]; 
    } 

    std::cout << "\n"; 

    return 0; 
} 

我如何打印出szColName，使得其僅在頂部出現一次，而不是它多次出現？ 嘗試這樣：

static int callback(void *NotUsed, int argc, char **argv, char **szColName) 
{ 
    int n = sizeof(szColName)/sizeof(szColName[0]); 
    for (int i = 0; i < n; i++) 
    { 
     cout.width(17); cout << left << szColName[i]; 
    } 
    printf("\n"); 
    for(int i = 0; i < argc; i++) 
    { 
     cout.width(17); cout << left << argv[i]; 
    } 

    std::cout << "\n"; 

    return 0; 
} 

但後輸出行值

Answer 1

您可能要聲明一個static bool內回調記錄是否已經打印出來的列名輸出每次。或者，如果您希望能夠將其復位......

如：

static bool firstline = true; 

static int callback(void *NotUsed, int argc, char **argv, char **szColName) 
{ 
if (firstline){ 
    int n = sizeof(szColName)/sizeof(szColName[0]);//this is incorrect but fixing 
               // it requires changing the prototype. 
                //See the comments below 
    for (int i = 0; i < n; i++) 
    { 
     cout.width(17); cout << szColName[i] << left; 
    } 
    printf("\n"); 
    firstline=false; 
} 
for(int i = 0; i < argc; i++) 
{ 
    cout.width(17); cout << argv[i] << left; 
} 

std::cout << "\n"; 

return 0; 
} 
int main(){ 
    for(int x=0;x<10;++x)callback(... , ... , ...); // give whatever argument you need to give 

    firstline = true; //reset the variable so that next time you call it, the col names will appear 
    for(int x=0;x<10;++x)callback(...,...,...);// now the col names will appear again. 
} 

---

我假設你提供將打印出的行和列名正確的。我只添加了一個變量來檢查是否需要打印列名。