这几天看到了fopen的参数设置。中文的那些真的是不能帮助精确理解。在网上发现了英文的,特附上:
FILE *fopen(const char *filename, const char *mode)
fopen opens the named file, and returns a stream, or NULL if the attempt fails. Legal values for mode include:
"r"
open text file for reading
"w"
create text file for writing; discard previous contents if any
"a"
append; open or create text file for writing at end of file
"r+"
open text file for update (i.e., reading and writing)
"w+"
create text file for update, discard previous contents if any
"a+"
append; open or create text file for update, writing at end
Update mode permits reading and writing the same file; fflush or a file-positioning function must be called between a read and a write or vice versa. If the mode includes b after the initial letter, as in "rb" or "w+b", that indicates a binary file. Filenames are limited to FILENAME_MAX characters. At most FOPEN_MAX files may be open at once.
其中+号表示可读可写,即上面的“更新模式”。
对“更新模式”:可以同时读写,但是必须有清空缓冲区函数或者文件定位函数。意思是在读或写之间得调用文件定位的相关函数,比如fseek,rewind等等。
经我测试确实是这样。
int main() { FILE *fp = fopen("1.txt", "r+"); char Rbuf[5], Wbuf[5] = "4321"; fread(Rbuf, sizeof(char), 4, fp); Rbuf[4] = '