如何在C ++中按字母顺序对标准输入字符串进行排序？

Question

#include <iostream> 
using namespace std;

int main (int argc, char **argv)
{
    int i = 0, j = 0;
    string temp;

    for (i = 1; i < argc; ++i)
    {
         for (j = i+1; j < argc; ++j)
         {
              if (argv[i] > argv[j])
              {
                   temp = argv[i];
                   argv[i] = argv[j];
                   argv[j] = temp;
              }
          }
     }
}

I don't know why but i am getting this Error when i compile it.

trial2.cpp:109:14: error: assigning to 'char *' from incompatible type 'string' (aka'basic_string, allocator >') argv[j] = temp; ^ ~~~~ //temp is my temporary string.

Answer 1

There are two errors in the code:

1. As @hyde pointed out, temp should be char* and not string
2. argv[i] > argv[j] looks like pointer comparison ie it will compare the value of the address rather than comparing the string. I suggest using strcmp methods for comparing two char* (then you need to #include <string> to use this method)

Suggested code (not sure if totally bug free or not, but hopefully it's the case):

#include <iostream>
#include <string>
using namespace std;

int main (int argc, char **argv)
{
    int i = 0, j = 0;
    char* temp;

    for (i = 1; i < argc; ++i)
    {
         for (j = i+1; j < argc; ++j)
         {
              if (strcmp(argv[i] , argv[j]) > 0)
              {
                   temp = argv[i];
                   argv[i] = argv[j];
                   argv[j] = temp;
              }
          }
     }
    for(i = 0; i < argc; i++){
        cout << argv[i]<< endl;
    }
} 

Note the final for loop is to check if the output is sorted. I tried your comparison argv[i] > argv[j] rather than strcmp and it does not seem to work on my machine.

Answer 2

Error spring up becouse it fails cast type string to char * . But it must work reversed (therefore your temp = argv[i]; does't fails). Don't write to argv (you can, but I do not recommend). Simple way: Copy argv to to some array of string before sorting: `

string *argv_strings = new string[argc - 1];
for(int i = 0; i < argc - 1; ++i)
{
    argv_strings[i] = new string(argv[i + 1]);
}

`

and work with argv_strings instead argv Do not forget delete pointer after.