c – fgets()的返回值

我刚刚开始使用C中的I / O.这是我的问题 – 我有一个文件,我从中读取了我的输入.然后我使用fgets()来获取缓冲区中的字符串,我以某种方式使用它.现在,如果输入对于缓冲区来说太短,即如果fgets()的第一次读取达到EOF,会发生什么. fgets()应该返回NULL(正如我在fgets()文档中读到的那样)？它似乎没有,我得到了正确的输入.除了我的feof(输入)并没有说我们已经达到了EOF.这是我的代码片段.

char    buf[BUFSIZ];
FILE    *input,*output;

input   = fopen(argv[--argc],"r");
output  = fopen(argv[--argc],"w");

/**
 *  If either of the input or output were unable to be opened
 *          we exit
 */
if (input == NULL) {
    fprintf(stdout,"Failed to open file - %s.\n",argv[argc + 1]);
    exit(EXIT_FAILURE);
}

if (output == NULL) {
    fprintf(stdout,argv[argc + 0]);
    exit(EXIT_FAILURE);
}

if (fgets(buf,sizeof(buf),input) != NULL) {
    ....
}

/**
 *  After the fgets() condition exits it is because,either -
 *      1) The EOF was reached.
 *      2) There is a read error.
 */
if (feof(input)) {
    fprintf(stdout,"Reached EOF.\n");
}
else if (ferror(input)) {
    fprintf(stdout,"Error while reading the file.\n");
}

解决方法

fgets()的文档没有说出你的想法：

从我的联机帮助页

fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading
stops after an EOF or a newline. If a newline is read,it is stored into the buffer. A terminating null byte (‘\0‘) is stored
after the last character in the buffer.

然后

gets() and fgets() return s on success,and NULL on error or when end of file occurs while no characters have been read.

我没有读到,因为说EOF将被视为错误条件并返回NULL.实际上它说只有在没有读取字符时发生EOF的情况下才会出现NULL.

POSIX标准(遵循不太容易访问的C标准)在这里：http://pubs.opengroup.org/onlinepubs/009695399/functions/fgets.html并声明：

Upon successful completion,fgets() shall return s. If the stream is at end-of-file,the end-of-file indicator for the stream shall be set and fgets() shall return a null pointer. If a read error occurs,the error indicator for the stream shall be set,fgets() shall return a null pointer,and shall set errno to indicate the error.

这清楚地表明,如果在调用时它实际上处于EOF状态,它将仅返回NULL,即如果读取任何字节,则不会返回NULL.

c – fgets()的返回值

解决方法

猜你在找的C&C++相关文章