c/c++读取文件

 #include <iostream>
 #include <string>
 #include <fstream>

 int main() {
     std::ifstream in_file("test.txt");
     std::string line;
     while ( getline(in_file, line) ) {
         std::cout << line;
     }
 }

不需要检查test.txt是否存在

下面的函数可以实现顺序读取文件，且限制每次读的最大行数

 #include <stdio.h>
 #include <iostream>
 #include <stdlib.h>

 const unsigned line_size = ;
 const unsigned max_line = ;

 bool read_file( FILE *p_file, unsigned line_num, unsigned data[] ) {

     if ( line_num > max_line ) {
         return false;
     }

     char buf[max_line][line_size];

     fread(buf, line_size, line_num, p_file);

     for(int i =  ; i < line_num; i++) {
         buf[i][line_size - ] = ;
         data[i] = atoi(buf[i]);
     }

     return true;
 }

 bool write_file( FILE *p_file, unsigned line_num, unsigned data[] ) {

     if ( line_num > max_line ) {
         return false;
     }

     char buf[max_line][line_size];

     for(int i =  ; i < line_num; i++) {
         itoa( data[i], buf[i],  );
         if ( i != line_num -  ) {
             buf[i][line_size - ] = '\n';
         }
     }

     fwrite( buf, , sizeof(buf) - , p_file );
 }

 void buble_sort(unsigned data[], unsigned num) {
     for( int i = ; i < num; i++ ) {
         for (int j = i + ; j < num; j++ ) {
             if ( data[i] > data[j] ) {
                 unsigned temp = data[i];
                 data[i] = data[j];
                 data[j] = temp;
             }
         }
     }
 }

 int main() {
     FILE *p_file = fopen("test.txt", "r");
     if ( NULL == p_file ) {
         return -;
     }

     unsigned data[];
     for ( int j = ; j < ; j++ ) {
         if ( read_file(p_file, , data) ) {
             buble_sort(data, );
             for ( int i = ; i < ; i ++ ) {
                 std::cout << data[i] << " ";
             }
             std::cout << std::endl;
             char out_file_name[];
             itoa(j, out_file_name, );
             FILE *p_file_out = fopen(out_file_name, "w");
             write_file(p_file_out, , data);
             fclose(p_file_out);
         }
     }
     fclose(p_file);

 }