使用Mmap第一个字符是错误的(Using Mmap first character is wrong)

使用Mmap我想从Hello，world改变文件的内容！世界上的Jello！

输入文件是Hello.txt，这是1行Hello，world！输出通常是'ello，world！输出应该是Jello，世界！运行程序pgm.exe hello.txt 1

关键的代码行是在程序结束时（也许某些东西是关键的，我只是不知道它）

感谢您的帮助

#include <stdio.h> #include <sys/types.h> #include <sys/mman.h> #include <stdlib.h> #include <fcntl.h> #include <sys/stat.h> #include <unistd.h> #include <signal.h> #include <string.h> void main(int argc, char *argv[]) { int fd, changes, i ; struct stat buf; char *the_file, *starting_string = "Jello,world!"; if (argc != 3) { printf("Usage: %s file_name #_of_changes\n", *argv); exit(1); } if ((changes = atoi(argv[2])) < 1) { printf("#_of_changes < 1\n"); exit(1); } if ((fd = open(argv[1], O_CREAT | O_RDWR, 0666)) < 0) { printf("open error on file %s\n", argv[1]); exit(1); } //write(fd, starting_string, strlen(starting_string)); /* Obtain size of file to be mapped */ if (fstat(fd, &buf) < 0) { printf("fstat error on file %s\n", argv[1]); exit(1); } /* Establish the mapping */ if ((the_file = mmap(0, (size_t)buf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)) == (caddr_t)-1){ printf("mmap failure\n"); exit(1); } printf("The file orginally contains:\n %s \n", the_file); *(the_file) = "Jello,world!"; printf("The file now contains:\n %s \n", the_file); exit(0); }

Using Mmap I want to change the contents of file from Hello,world! to Jello, world!

The input file is Hello.txt which is 1 line Hello,world! The output is usually `ello,world! The output should be Jello,world! to run the program pgm.exe hello.txt 1

the critical lines of code are at end of program (maybe something is is critical and I just dont know it)

thank you for your help

#include <stdio.h> #include <sys/types.h> #include <sys/mman.h> #include <stdlib.h> #include <fcntl.h> #include <sys/stat.h> #include <unistd.h> #include <signal.h> #include <string.h> void main(int argc, char *argv[]) { int fd, changes, i ; struct stat buf; char *the_file, *starting_string = "Jello,world!"; if (argc != 3) { printf("Usage: %s file_name #_of_changes\n", *argv); exit(1); } if ((changes = atoi(argv[2])) < 1) { printf("#_of_changes < 1\n"); exit(1); } if ((fd = open(argv[1], O_CREAT | O_RDWR, 0666)) < 0) { printf("open error on file %s\n", argv[1]); exit(1); } //write(fd, starting_string, strlen(starting_string)); /* Obtain size of file to be mapped */ if (fstat(fd, &buf) < 0) { printf("fstat error on file %s\n", argv[1]); exit(1); } /* Establish the mapping */ if ((the_file = mmap(0, (size_t)buf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0)) == (caddr_t)-1){ printf("mmap failure\n"); exit(1); } printf("The file orginally contains:\n %s \n", the_file); *(the_file) = "Jello,world!"; printf("The file now contains:\n %s \n", the_file); exit(0); }