我写这个函数是从文件中读取一行:
const char *readLine(FILE *file) {
if (file == NULL) {
printf("Error: file pointer is null.");
exit(1);
}
int maximumLineLength = 128;
char *lineBuffer = (char *)malloc(sizeof(char) * maximumLineLength);
if (lineBuffer == NULL) {
printf("Error allocating memory for line buffer.");
exit(1);
}
char ch = getc(file);
int count = 0;
while ((ch != '\n') && (ch != EOF)) {
if (count == maximumLineLength) {
maximumLineLength += 128;
lineBuffer = realloc(lineBuffer, maximumLineLength);
if (lineBuffer == NULL) {
printf("Error reallocating space for line buffer.");
exit(1);
}
}
lineBuffer[count] = ch;
count++;
ch = getc(file);
}
lineBuffer[count] = '\0';
char line[count + 1];
strncpy(line, lineBuffer, (count + 1));
free(lineBuffer);
const char *constLine = line;
return constLine;
}
该函数正确地读取文件，使用printf我看到constLine字符串也被正确读取。
然而，如果我像这样使用函数:
while (!feof(myFile)) {
const char *line = readLine(myFile);
printf("%s\n", line);
}
Printf输出胡言乱语。为什么?
实现从文件中读取和获取内容的方法(input1.txt)
#include <stdio.h>
#include <stdlib.h>
void testGetFile() {
// open file
FILE *fp = fopen("input1.txt", "r");
size_t len = 255;
// need malloc memory for line, if not, segmentation fault error will occurred.
char *line = malloc(sizeof(char) * len);
// check if file exist (and you can open it) or not
if (fp == NULL) {
printf("can open file input1.txt!");
return;
}
while(fgets(line, len, fp) != NULL) {
printf("%s\n", line);
}
free(line);
}
希望这对你有所帮助。编码快乐!
实现从文件中读取和获取内容的方法(input1.txt)
#include <stdio.h>
#include <stdlib.h>
void testGetFile() {
// open file
FILE *fp = fopen("input1.txt", "r");
size_t len = 255;
// need malloc memory for line, if not, segmentation fault error will occurred.
char *line = malloc(sizeof(char) * len);
// check if file exist (and you can open it) or not
if (fp == NULL) {
printf("can open file input1.txt!");
return;
}
while(fgets(line, len, fp) != NULL) {
printf("%s\n", line);
}
free(line);
}
希望这对你有所帮助。编码快乐!
在readLine函数中，返回一个指向行数组的指针(严格地说，是指向该行数组第一个字符的指针，但这里的区别无关紧要)。由于它是一个自动变量(即，它“在堆栈上”)，当函数返回时，内存将被回收。你看到的是乱七八糟的东西，因为printf把它自己的东西放到了堆栈上。
您需要从函数返回一个动态分配的缓冲区。你已经有一个了，它是lineBuffer;你所要做的就是把它截断成所需的长度。
lineBuffer[count] = '\0';
realloc(lineBuffer, count + 1);
return lineBuffer;
}
ADDED(对评论中后续问题的回应):readLine返回一个指向组成该行的字符的指针。这个指针是处理该行内容所需要的指针。当你用完这些字符占用的内存时，你也必须通过它来释放内存。下面是如何使用readLine函数:
char *line = readLine(file);
printf("LOG: read a line: %s\n", line);
if (strchr(line, 'a')) { puts("The line contains an a"); }
/* etc. */
free(line);
/* After this point, the memory allocated for the line has been reclaimed.
You can't use the value of `line` again (though you can assign a new value
to the `line` variable if you want). */
您应该使用ANSI函数来读取一行，例如。fgets。调用后，你需要在调用上下文中使用free()，例如:
...
const char *entirecontent=readLine(myFile);
puts(entirecontent);
free(entirecontent);
...
const char *readLine(FILE *file)
{
char *lineBuffer=calloc(1,1), line[128];
if ( !file || !lineBuffer )
{
fprintf(stderr,"an ErrorNo 1: ...");
exit(1);
}
for(; fgets(line,sizeof line,file) ; strcat(lineBuffer,line) )
{
if( strchr(line,'\n') ) *strchr(line,'\n')=0;
lineBuffer=realloc(lineBuffer,strlen(lineBuffer)+strlen(line)+1);
if( !lineBuffer )
{
fprintf(stderr,"an ErrorNo 2: ...");
exit(2);
}
}
return lineBuffer;
}
