c++ - 调试断言失败，表达式:(unsigned)(c +1)<= 256提问c++

Question

我要计算空格数。据我了解，编译器在这一行发誓 isspace(s [step])!= 0 。但是有时代码会启动，并且没有错误。我不知道为什么会这样。

char s[] = "So she was considering";

int number_space = 0, step = 0;
int length_string = strlen(s);

while(strlen(s) != step){
    if(isspace(s[step]) != 0){ 
        number_space++;
    }
step++;
}

cout << number_space;

Answer 1

你必须写

if ( isspace( static_cast<unsigned char>( s[step] ) ) != 0 ){ 

要么

if ( isspace( ( unsigned char )s[step] ) != 0 ){ 

否则，通常表达式s [step]会产生负值。

此代码段

int number_space = 0, step = 0;
int length_string = strlen(s);

while(strlen(s) != step){
    if(isspace(s[step]) != 0){ 
        number_space++;
    }
step++;
}

可以更简单地重写

size_t number_space = 0;

for ( size_t i = 0; s[i] != '\0'; i++ )
{
    if ( isspace( static_cast<unsigned char>( s[i] ) ) )
    {
        number_space++;
    } 
}   

那就是没有必要在循环的情况下调用strlen。