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Top Forums Programming C: inputting string of unknown length Post 303040993 by DevuanFan on Monday 11th of November 2019 08:58:45 PM
Old 11-11-2019
Andrew, thank you so much for your beautiful explanation. I understand the issue and can confirm that this works exactly as expected:

Code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define SIZE 4

int main(void)
{
	int mem = SIZE;
	char *str = malloc(mem); // let's keep str pointing to beginning of string...
	char *next_read = str; // ...and next_read pointing to where next character should go

	fgets(next_read, mem, stdin);
	printf("str is now %s\n", str);

	while(str[strlen(str)-1] != '\n') // if we got whole string, the last char will be '\n'
	{
		mem += SIZE;
		str = realloc(str, mem); 
		next_read = str + strlen(str);
		fgets(next_read, SIZE+1, stdin); // read the rest (hopefully) of the line into the new space
		printf("str is now %s\n", str);
	}

	printf("final str is %s", str);
	// free(str);
	return 0;
}

Code:
bruno@thinkpad:~/Desktop444$ gcc getstring.c
bruno@thinkpad:~/Desktop445$ ./a.out 
I love linux and the C programming language
str is now I l
str is now I love 
str is now I love linu
str is now I love linux an
str is now I love linux and th
str is now I love linux and the C 
str is now I love linux and the C prog
str is now I love linux and the C programm
str is now I love linux and the C programming 
str is now I love linux and the C programming lang
str is now I love linux and the C programming language
str is now I love linux and the C programming language

final str is I love linux and the C programming language

It is strange that realloc() reallocates in situ at first, then not. Knowing that there are no guarantees was the key to the mystery. THANK YOU Smilie
This User Gave Thanks to DevuanFan For This Post:
 

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GLSHADERSOURCE(3G)						   OpenGL Manual						GLSHADERSOURCE(3G)

NAME
glShaderSource - Replaces the source code in a shader object C SPECIFICATION
void glShaderSource(GLuint shader, GLsizei count, const GLchar **string, const GLint *length); PARAMETERS
shader Specifies the handle of the shader object whose source code is to be replaced. count Specifies the number of elements in the string and length arrays. string Specifies an array of pointers to strings containing the source code to be loaded into the shader. length Specifies an array of string lengths. DESCRIPTION
glShaderSource sets the source code in shader to the source code in the array of strings specified by string. Any source code previously stored in the shader object is completely replaced. The number of strings in the array is specified by count. If length is NULL, each string is assumed to be null terminated. If length is a value other than NULL, it points to an array containing a string length for each of the corresponding elements of string. Each element in the length array may contain the length of the corresponding string (the null character is not counted as part of the string length) or a value less than 0 to indicate that the string is null terminated. The source code strings are not scanned or parsed at this time; they are simply copied into the specified shader object. NOTES
OpenGL copies the shader source code strings when glShaderSource is called, so an application may free its copy of the source code strings immediately after the function returns. ERRORS
GL_INVALID_VALUE is generated if shader is not a value generated by OpenGL. GL_INVALID_OPERATION is generated if shader is not a shader object. GL_INVALID_VALUE is generated if count is less than 0. ASSOCIATED GETS
glGetShader() with arguments shader and GL_SHADER_SOURCE_LENGTH glGetShaderSource() with argument shader glIsShader() SEE ALSO
glCompileShader(), glCreateShader(), glDeleteShader() COPYRIGHT
Copyright (C) 2003-2005 3Dlabs Inc. Ltd. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/. AUTHORS
opengl.org opengl.org 06/10/2014 GLSHADERSOURCE(3G)
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