Call system UNIX - File copy in C -


i try create copy of source file target file empty.

the algorithm is: read stdin , write source file, read on file , write text in target file.

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h>  #define buffsize 8192  int main(){     int fdsource, fdtarget;     int n, nr;     char buff[buffsize];      fdsource = open("source.txt", o_rdwr | o_creat, s_irusr | s_iwusr); // create , open source file in read/write     if (fdsource < 0){         printf("source file open error!\n");         exit(1);     }      fdtarget = open("target.txt", o_wronly | o_creat, s_irusr | s_iwusr); // create , open source file in write     if (fdtarget < 0){         printf("target file open error!\n");         exit(1);     }      printf("\ninsert text:\n");     while ((n = read(stdin_fileno, buff, buffsize)) > 0){ // read stdin , write source file         if ((write(fdsource, buff, n)) != n){             printf("source file write error!\n");             exit(1);         }     }      while ((read(fdsource, buff, n)) > 0){ // read source file , write target file         if ((write(fdtarget, buff, n)) != n){             printf("source file open error!\n");             exit(1);         }     }     close(fdsource);     close(fdtarget);     exit(0);     return 0; }

the problem code "you have opened both file in initial stage". solve problem open source file in write mode , write data, close , reopen source file in read mode, open target file in write mode. modified code given below , not tested

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h>  #define buffsize 8192  int main(){     int fdsource, fdtarget;     int n;     char buff[buffsize];      fdsource = open("source.txt", o_rdwr | o_creat, s_irusr | s_iwusr); // create , open source file in read/write     if (fdsource < 0){         printf("source file open error!\n");         exit(1);     }     printf("\ninsert text:\n");     while ((n = read(stdin_fileno, buff, buffsize)) > 0){ // read stdin , write source file         if ((write(fdsource, buff, n)) != n){             printf("source file write error!\n");             exit(1);         }     }      close(fdsource);     fdsource = open("source.txt", o_rdwr | o_creat, s_irusr | s_iwusr); // create , open source file in read/write     if (fdsource < 0){         printf("source file open error!\n");         exit(1);     }      fdtarget = open("target.txt", o_wronly | o_creat, s_irusr | s_iwusr); // create , open source file in write     if (fdtarget < 0){         printf("target file open error!\n");         exit(1);     }      while ((read(fdsource, buff, n)) > 0){ // read source file , write target file         if ((write(fdtarget, buff, n)) != n){             printf("source file open error!\n");             exit(1);         }     }     close(fdsource);     close(fdtarget);     exit(0);     return 0; }

if wrong anywhere use logic mentioned above.


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