CODEWITHSUNDEEP
c++
user466444
user466444

Reputation: 489

sort of arguments

i have following code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int comp(const void *a, const void *b){
char *const *aa=a;
char *const *bb=b;
return strcmp(*aa,*bb):


}
int main(int argc,char **argv){

int i;
  qsort(argv+1,argc-1,sizeof *argv,comp);
   for (i=1;i<argc;i++)
       printf("i: %d==> '%s'\n",i,argv[i]);
   return 0;


}

but here is errors

Error   1   error C2440: 'initializing' : cannot convert from 'const void *' to 'char *const *' c:\users\student\documents\visual studio 2008\projects\sort_argv\sort_argv\sort_argv.cpp    5   sort_argv
Error   2   error C2440: 'initializing' : cannot convert from 'const void *' to 'char *const *' c:\users\student\documents\visual studio 2008\projects\sort_argv\sort_argv\sort_argv.cpp    6   sort_argv

Error 3 error C2143: syntax error : missing ';' before ':' 

c:\users\student\documents\visual studio 2008\projects\sort_argv\sort_argv\sort_argv.cpp    7   sort_argv

Error 4 error C2143: syntax error : missing ';' before ':' 

c:\users\student\documents\visual studio 2008\projects\sort_argv\sort_argv\sort_argv.cpp    7   sort_argv

please help

Upvotes: 1

Views: 779

Answers (4)

Konrad Rudolph
Konrad Rudolph

Reputation: 545598

In C++, use sort instead of qsort. Furthermore, the elements of argv must not be mutated since they are (implicitly, for C backwards compatibility) declared const. Therefore, you need to copy them somewhere else: (Apparently not true.)

#include <string>
#include <vector>
#include <algorithm> // for sort

int main(int argc, char const* argv[]) {
    std::vector<std::string> args(argv, argv + argc);
    std::sort(args.begin(), args.end());
}

(Notice that this solution uses string and vector instead of C strings and C-style arrays where possible. That’s not necessary but it makes the code much easier and shorter.)

Upvotes: 4

MSalters
MSalters

Reputation: 179849

Well, are you using C or C++ ? You've got a valid C program (minus the typo : instead of ;). Yet you name it ".cpp", and initially tagged the question only "C++" (fixed now). If you don't tell it otherwise, Visual Studio's compiler will compile ".cpp" files as C++. And your program is not valid C++.

In C++, you would use std::sort, not qsort. It has a different interface, and const void* is not needed. Then your problem will disappear.

Upvotes: 4

Jon Cage
Jon Cage

Reputation: 37478

Try replacing:

int comp(const void *a, const void *b){
    char *const *aa=a;
    char *const *bb=b;
    return strcmp(*aa,*bb):
}

with: 

int comp(const void *a, const void *b){
    const char* aa = (const char*)a;
    const char* bb= (const char*)b;
    return strcmp(*aa,*bb):
}

..to solve the pointer conversion problem.

Upvotes: 0

Cedric H.
Cedric H.

Reputation: 8298

I think your question is not well asked, and it shows that you didn't even read your code carefully before asking. However, one obvious mistake is that:

return strcmp(*aa,*bb):  // : instead of ;

Upvotes: 2

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