C逐行读取文件
C逐行读取文件
提问于 2010-08-17 18:08:59
我编写此函数是为了从文件中读取一行：
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;
}函数正确地读取了文件，并且使用printf我看到constLine字符串也被正确地读取了。
但是，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？
回答 11
Stack Overflow用户
发布于 2010-08-17 19:03:31
如果您的任务不是发明逐行读取函数，而只是逐行读取文件，则可以使用涉及getline()函数的典型代码片段(请参阅手册页here)：
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
FILE * fp;
char * line = NULL;
size_t len = 0;
ssize_t read;
fp = fopen("/etc/motd", "r");
if (fp == NULL)
exit(EXIT_FAILURE);
while ((read = getline(&line, &len, fp)) != -1) {
printf("Retrieved line of length %zu:\n", read);
printf("%s", line);
}
fclose(fp);
if (line)
free(line);
exit(EXIT_SUCCESS);
}Stack Overflow用户
发布于 2016-08-31 05:47:47
FILE* filePointer;
int bufferLength = 255;
char buffer[bufferLength];
filePointer = fopen("file.txt", "r");
while(fgets(buffer, bufferLength, filePointer)) {
printf("%s\n", buffer);
}
fclose(filePointer);Stack Overflow用户
发布于 2014-10-23 05:35:47
//open and get the file handle
FILE* fh;
fopen_s(&fh, filename, "r");
//check if file exists
if (fh == NULL){
printf("file does not exists %s", filename);
return 0;
}
//read line by line
const size_t line_size = 300;
char* line = malloc(line_size);
while (fgets(line, line_size, fh) != NULL) {
printf(line);
}
free(line); // dont forget to free heap memory页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/3501338
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