C++ setprecision不显示数字

我有以下函数片段：

bool A_AbstractTester_Actor::Equals( int lineNumber, T_String valueText, double value, T_String expectedText, double expected, double accuracy )
{
    ...
    v_FailedText << std::setprecision(8) << "\nLine " << lineNumber  
     << ": EQUALS_DOUBLE FAILED, Value '" << valueText << "' (" << value 
     << "), Expected '" << expectedText << "' (" << expected << ")\n";

我所期望的是：

Line 242: EQUALS_DOUBLE_FAILED, Value 'step' (0.00000000), Expected '1.0' (1.00000000)

你应该使用操纵器

bool A_AbstractTester_Actor::Equals( int lineNumber, T_String valueText, double value, T_String expectedText, double expected, double accuracy )
{
    ...
    v_FailedText << std::fixed << std::setprecision(8) "\nLine " << lineNumber  
     << ": EQUALS_DOUBLE FAILED, Value '" << valueText << "' (" << value 
     << "), Expected '" << expectedText << "' (" << expected << ")\n";

bool A_AbstractTester_Actor:：Equals（整数行号、T_字符串值文本、双值、T_字符串预期文本、双预期、双精度）
{
...
v_FailedText If memory service其中一些操纵器调用非常短暂。如果在打印浮点值之前执行setprecision操纵器，它是否仍然不起作用？
bool A_AbstractTester_Actor::Equals( int lineNumber, T_String valueText, double value, T_String expectedText, double expected, double accuracy )
{
    ...
    v_FailedText << std::fixed << std::setprecision(8) "\nLine " << lineNumber  
     << ": EQUALS_DOUBLE FAILED, Value '" << valueText << "' (" << value 
     << "), Expected '" << expectedText << "' (" << expected << ")\n";