从命令提示符运行程序并在 C++ 中使用 argv;
我编写了一个程序，它从 argv[1] 获取文件名并对其进行操作。 从 Visual Studio 进行调试时，我从项目选项>>调试>>命令参数传递文件名，它工作正常并正确打印所有结果。
但是，当从命令提示符尝试时，我转到项目/调试的目录，我输入
program
它工作正常，并在同一窗口中打印 “没有有效的输入文件” （这是我的错误处理技术）
但当我输入时
program test.txt
它什么也没做。我认为代码没有问题，因为它在调试器中工作得很好。
代码 ：
int main(int argc, char *argv[])
{
int nLines;
string str;
if(argv[1]==NULL)
{
std::cout << "Not valid input file" << endl;
return 0 ;
}
ifstream infile(argv[1]);
getline(infile,str);
nLines = atoi(str.c_str());//get number of lines
for(int line=0 ;line < nLines;line++)
{
//int currTime , and a lot of variables ..
//do a lot of stuff and while loops
cout << currTime <<endl ;
}
return 0 ;
}
I have written a program that takes the filename from argv[1] and do operations on it .
When debugging from visual studio I pass the filename from project options>>debugging>>command arguments and It works fine and prints all results correctly .
But when trying from the command prompt , I go to the dir of project/debug the I type
program
It works fine and prints "No valid input file" in the same window (Which is my error handling technique)
but when i type
program test.txt
It just does nothing . I think no problem in code because it works fine from the debugger .
Code :
int main(int argc, char *argv[])
{
int nLines;
string str;
if(argv[1]==NULL)
{
std::cout << "Not valid input file" << endl;
return 0 ;
}
ifstream infile(argv[1]);
getline(infile,str);
nLines = atoi(str.c_str());//get number of lines
for(int line=0 ;line < nLines;line++)
{
//int currTime , and a lot of variables ..
//do a lot of stuff and while loops
cout << currTime <<endl ;
}
return 0 ;
}
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评论（3）
您不检查文件是否已成功打开，getline 是否返回错误代码，或者字符串到整数的转换是否未失败。如果发生任何这些错误（我猜是这种情况），
nLines将等于0，不会执行任何循环，程序将退出并返回代码0 。You don't check if file was successfully opened, whether getline returned error code or not, or if string to integer conversion didn't fail. If any of those error occur, which I guess is the case,
nLineswill be equal to0, no cycles will be performed and program will exit with return code0.这段代码对我在命令行上运行来说是正确的。
输出：
顺便说一句，这段代码充其量是危险的：
您应该在尝试取消引用可能为野的指针之前检查 argc 的值。
This code worked correctly for me running on the command line.
Output :
By the way, this code is dangerous, at best:
You should probably be checking the value of
argcbefore attempting to dereference a possibly-wild pointer.该文件可能包含无效的数字第一行（可能以空格或 BOM 开头） 。
这可以解释没有输出，因为如果 nLines == 0 则不应有输出
The file probably contains an invalid numeric first line (perhaps starting with a space or the BOM).
That would explain no output, since if
nLines == 0no output should be expected